woodworks

Brightness and Exposure are also present in Lightroom and Photoshop (with similar meanings), although maybe not as obvious?
For a short explanation, see: https://digital-photography-school.com/exposure-vs-brightness-vs-fill-light/
Completely inaccurate summary: exposure brightens everything, brightness has more effect on the midtones.
I suspect image editing is getting to the stage where there are so many controls we can't learn (or at least remember and use) everything.
 
I don't yet have an iPad, but from the Windows help for Affinity Photo (I think the iPad has similar help built in, but I don't know how it compares):
Sync Before—updates the 'Before' view using the settings applied in the 'After' view. Sync After—removes all the settings applied in the 'After' view to return the image to the 'Before' view. Swap—switches the applied settings of the 'Before' and 'After' views. So, as I understand it, somewhat like Undo/Redo but using side-by-side images to compare results.
These also exist in Lightroom as graphical icons down the bottom: https://i0.wp.com/digital-photography-school.com/wp-content/uploads/2010/07/brightness_step2.jpg

Did you try "disable Embed Metadata"? I had an earlier question on the same thing, that was suggested and it worked for me.

Add another request for arrowheads. But keep up the good work. You're getting closer.

I very much would like to buy this app, mainly because I would love to jettison Illustrator from my workflow before some future Mac OS renders my CS5 suite unusable. But right now Designer is not yet there for me.
 
I do technical illustration (patent drawings), and so my needs are quite different from what seems to be your target customer. Among the tools that I cannot do without:
 
1. Tiled fills — I need to fill enclosed areas with a variety of different patterns, from hash lines to environmental patterns such as wood, glass, sand, concrete, metal, plastic, etc. In many cases, I need to create my own patterns and cannot rely on "canned" fills provided by other designers.
 
2. Dashed lines — I need to be able set the length of the lines and spaces.
 
3. Arrowheads — I need to be able to edit their shape and size.
 
4. Blended objects — I need to be able to create complex, grouped shapes, and then distribute them along a path.
 
I work only in black and white, so any color features are wasted on me. And I need to be able to import .dxf and .dwg files from CAD programs and maintain their editablity. These are minimum requirements for me, and I hope that you will consider eventually adding some of the tools that those of us who work in the technical illustration field will find useful. In the mean time, best of luck to you!