R C-R

Tip: Look in the status bar at the bottom of the document window. When the pointer is over one of the control handles at the ends of the gradient, you will see among other items "⇧+⌃ to rotate fill." Those are the Mac icons for the Shift & Control keys.

Alternately, if you mean to change the number of points (vertexes) of the polygon, you can do that by changing the number shown in the Sides: field of the context toolbar.

Same here. In fact, if I used Save on a newly created file in APub I would find it extremely odd if it saved it as an *.afphoto or as any other file type. It would be like using Save with a new project in any other creative app & having it saved as something other than as its native file type.

I was using Safari on a Mac & could see also the videos directly on this page.

Same for me running Catalina (& everything else my sig mentions) -- file opens fine, although it is composed mostly of short curves.

Some of us have been waiting almost a decade for any meaningful progress on the low contrast issues that we have been reporting almost since day one. I would like to think that at least some of them will finally be fixed before V3 is released, but it really does seem like the developers simply do not care about doing that ... & I have no faith that anything significant will change with the release of V3.

It can also be transparent, which displays as a greyscale checkerboard pattern.

Not entirely sure what you are trying to show but it looks like in the Designer Persona you have detached (undocked) the right studio panel so it is floating over the document window, while in the Export Persona it is docked.

They are invisible simply because their color & the background behind them is nearly the same -- IOW, yet another example of the low contrast issue.

Nonsense. It is just a matter of going through the UI & making everything that appears with a grey level too nearly the same as its background to a more contrasting shade of grey. It used to be possible in the oldest Mac versions because they followed the old Mac conventions of separate resources for active selections, inactive ones, & ones that could not be selected ("greyed out") & users could actually access them with tools Apple provided to anyone & change them to whatever they wanted (I did that myself with a few things like the tiny triangles in the tools panel) but they changed all that for reasons unknown.

<sigh> As I have mentioned I have tried every possible setting that could possibly affect the contrast of UI elements on my Mac, & first started doing this back around 10 years ago when there was no light UI mode & just AD for Macs. I can assure you that this is not an issue of any incorrectly set display options. It is, & always has been, a problem with how the Mac versions of the Affinities display low contrast versions certain UI elements like some of the buttons, some UI text elements, etc. Please, just look carefully at the first post of the topic, & at my screenshot of a tab. It doesn't get any better no matter how anything is adjusted, only worse.

Just FYI, as has been mentioned, the first version of AD was released in 2014 & was only for Macs. The first Windows version was released a bit over 2 years later (see for example https://en.wikipedia.org/wiki/Affinity_Designer for more about this.) But the low contrast Dark Mode UI problem that is shown in the OP of this thread is among the ones Mac Users have been complaining about for nearly 10 years now, & remain unresolved. So I do not understand why Windows users keep saying it is not a problem for them. They are not running the OS that exhibits these issues!!!

Just compare what the screenshots of the Mac UI in this (among many other) topics show with what you see if you switch to the Dark Mode on your Windows machine. For instance, look at the very first post & see if you can spot the close x in either tab. Or examine what I showed in a closeup of a tab with everything available set to the maximum contrast the Mac versions allow. If you do not think that is a problem I do not know what to say to you.

The x was not singled out as one of the several contrast issues but there have been complaints about low contrast making the UI difficult to use since the first release of AD for Macs. This includes the text contrast adjustment not changing anything in some parts of the UI (including in tabs) & much more, a few of which have been mentioned here.

You can get a very rough idea of what was adjusted by checking the Histogram panel as you apply one of the auto filters, but there isn't a way to get more than that. As has been mentioned, they are really useful only for quick & dirty corrections.