1.) Yeah it would be nice if Flags like this would not be hardcoded / predefined. Alternatively: Make the File with Pre-Definitions easily available and editable. DGUI obviously needs to be set depending on what is defined in the Project File (or wherever you store that).
2.) Accessibility Support: IF I would end up using Upp (still in the Final Test Phase) I would try to "get my Feet wet" and would love to help to implement this - if I would be able too and someone would show me where to start. For the foreseeable Future, my App needs to Support the old Windows 7+ Accessibility API as well (And I am also targeting Linux). Even as those Windows Versions are "Dead", they will be heavily used for the next couple years. And yes, I am aware that an Implementation and thorough testing of those API's will take many Months.
3.) Unicode: I would probably use ICU if I would have a urgent short-term need of modern Unicode / things not supported in the current Implementation.
4.) Debugger: Can not help you with that. This is way over my head. Simple Hobby Developer.
5.) C++ Parser: The more the better But what I really miss already in the Editor:
* No Text selected / marked: CTRL+SHIFT+Arrow Down or Arrow Up: Move the current single Line of Text (in which the Cursor sits) up or down
* Multiple Lines of Text selected: CTRL+SHIFT+Arrow Down or Arrow Up: Same but moves thew whole selected Textblock up or down
BTW: I had no Idea Upp existed until 2018:
People started to get annoyed with how Digia (The Company behind Qt - for those who do not know) CEO's are handling things.
On the official Interest-Mailing List, a Freelancer mentioned Upp (and other) as a possible Alternative. That is how I found you. I was really surprised that are nearly as old as Qt (if I remember correctly).
For a Core Team of 2 (3?) People: I take off my nonexistent Hat and say: I find some things to get used to but: Congratulations on how far you have come! Especially without any big Funding like other Projects had or still have.
But back to the Topic: Thanks four answers and for also pointing out (some) of the weaknesses of Upp. That is what I love to see!