R C-R

I wonder if the OP really is asking about the workspace background color rather than the canvas color. That can be set in Preferences > User Interface. Only to greyscale values are supported but black is a grey so that would do it.

In AP did you try this:
Make your marching ants selection using any of the selection tools Enable Quick Mask from the toolbar (or with the "Q" keyboard shortcut Switch to the Move Tool You should now be able to use the bounding box resize handles or the Transform panel to adjust the size (or move, rotate, or shear the selection around on the canvas) Exit Quick Mask mode to continue  

Only closed shapes have insides & outsides. Are your lines closed shapes?
EDIT: @Brian_J beat me to it!

Yes, I did not consider all the possibilities when rasterizing a pixel layer, but sometimes it does do nothing so at least in those cases there is no need to replace anything & thus no programatic reason to remove the lock.

Possibly because the OP asked about non-rectangular pages in Affinity Publisher, not artboards?

3 snapping points
 

You need to convert the circle to a text path & enter the text on it. But from what I can tell the "B" shape you want is created from two lines of characters (two paragraphs) so I have my doubts that there is any easy way to do this in Affinity.

The CMD key has to be pressed only when releasing the mouse button at the end of the drag to copy the dragged object, which I find a bit weird. I would prefer that it worked like the option key does now, but maybe that is just me.

In Preferences Interface, there is an option to show Undo & Redo buttons. Enable that & they will appear at the bottom right of the screen (as < & > symbols). I find that much easier to use, with or without using the Apple Pencil.

I think there should be some indication of that, perhaps with a tooltip popup, right there in the UI, because as it is it is far from obvious.

Regardless of the software you end up using, doing things like removing the background is often far from simple. Even apps that use machine learning (so called "artificial intelligence") to determine what should be considered part of the background do a reasonable job only for the kind of images they have been trained on, & often need a lot of touchup work to get the edges right.

I think we all can understand that you are not happy that you would have to pay more to get both the Mac & Windows versions.
But perhaps you can understand that many of us who do not need both would be unhappy if we had to pay more so you could pay less.

It is much more complicated to develop app versions for both Windows and Macs because there are so many fundamental differences in how they work "under the hood." They use different windowing models, different memory management schemes, different driver abstractions, etc.
This means the costs of developing one version does not cover the costs of developing the other, so one way or another Serif needs to set the purchase price to cover their development costs plus enough profit to keep the doors open. They could charge more for a multi-platform license, & perhaps even more for one that covered more than one or two devices, or they could do what they have done & license each platform individually, with a very generous policy for how many devices of that platform type the license covers.
Their choice means users who do not need or want versions for all three platforms are not subsidizing those who do.

Regardless of the software you end up using, doing things like removing the background is often far from simple. Even apps that use machine learning (so called "artificial intelligence") to determine what should be considered part of the background do a reasonable job only for the kind of images they have been trained on, & often need a lot of touchup work to get the edges right.

I think we all can understand that you are not happy that you would have to pay more to get both the Mac & Windows versions.
But perhaps you can understand that many of us who do not need both would be unhappy if we had to pay more so you could pay less.

I think we all can understand that you are not happy that you would have to pay more to get both the Mac & Windows versions.
But perhaps you can understand that many of us who do not need both would be unhappy if we had to pay more so you could pay less.

It was more than a wish list but less than a guarantee that anything on it would make it into the app 'soonish' if ever. For example, some things on it were being worked on when they were added but ended up being shelved because they caused too many hard to diagnose & fix bugs in the existing code.

I think we all can understand that you are not happy that you would have to pay more to get both the Mac & Windows versions.
But perhaps you can understand that many of us who do not need both would be unhappy if we had to pay more so you could pay less.

There are many apps that are only available for Windows or Macs but not for both.
But aside from that, consider all the apps that are cross-platform that you have to rent to use because you cannot buy them outright or if you can the perpetual license is very expensive, & those that are cross-platform but strictly limit the total number of devices they can be used on, often to just 2 devices.

It is much more complicated to develop app versions for both Windows and Macs because there are so many fundamental differences in how they work "under the hood." They use different windowing models, different memory management schemes, different driver abstractions, etc.
This means the costs of developing one version does not cover the costs of developing the other, so one way or another Serif needs to set the purchase price to cover their development costs plus enough profit to keep the doors open. They could charge more for a multi-platform license, & perhaps even more for one that covered more than one or two devices, or they could do what they have done & license each platform individually, with a very generous policy for how many devices of that platform type the license covers.
Their choice means users who do not need or want versions for all three platforms are not subsidizing those who do.

There are many apps that are only available for Windows or Macs but not for both.
But aside from that, consider all the apps that are cross-platform that you have to rent to use because you cannot buy them outright or if you can the perpetual license is very expensive, & those that are cross-platform but strictly limit the total number of devices they can be used on, often to just 2 devices.

It is much more complicated to develop app versions for both Windows and Macs because there are so many fundamental differences in how they work "under the hood." They use different windowing models, different memory management schemes, different driver abstractions, etc.
This means the costs of developing one version does not cover the costs of developing the other, so one way or another Serif needs to set the purchase price to cover their development costs plus enough profit to keep the doors open. They could charge more for a multi-platform license, & perhaps even more for one that covered more than one or two devices, or they could do what they have done & license each platform individually, with a very generous policy for how many devices of that platform type the license covers.
Their choice means users who do not need or want versions for all three platforms are not subsidizing those who do.

I think the brushes you want can be downloaded via this dropbox link (mentioned in this post by staffer @Callum). Specifically, the brush shown in your post is the Embroidery brush in the Vector Brushes > Image - 1.6 set. 

What I mean is there is no provision to make one.  There is for Break Curve & Join Curves in the Node Tool section of keyboard preferences, but not for the other 2 "Action" items.