Uhhh, I can’t remember what I did 3 days ago, let alone 3 months ago 
“bubble in bubble in bubble in bubble” yeah I was afraid of that.
Not really sure what you’re up to, transparency will make things slower and composite I believe is the old doublebuffer.
As for “Modern UI for Windows 11” I’m not really sure why its noted as Windows 11 as WinUI 3 (its actual name) is for Windows 10 1809 and above, I hope this is just a typo on the roadmap. I also hope it helps with your issues when it arrives.
Well, your problem IS related to UI elements, te OVERUSE of them. Xojo is not designed for that on windows, but to be fair, I dont think any tool is designed for that.
As I said before, you are breaking the design recommendations Xojo had in place for many many years so to be reallistic, dont expect they to change all the framework to acommodate your app design.
And as I said some months ago, your app could run ok in windows with some refactoring.
As for the Modern UI, who knows, could be the same with new classes, or could be fast enought to acommodate your overuse of UI elemments.
Thank you! May be I missed something - could you please tell me more about these recommendations? I do not know anything about them - what and where? Even if I Google them …
What confuses me a bit is that everything works perfect on the Mac. And Xojo says it is cross platform. Obviously it is not - or not really, or not in complete.
The only real recommendation (or conclusion if you want) for me is: Develop on Windows and then create a Mac App out of that, but never vice versa.
And yes, you are right - some refactoring may resolve these issues. And again thank you for your valuable answers! After more than two years I am not sure if I am really ready for that. My App consists out of two separate areas: UI and Processing. Processing runs completely headless on a database. But the UI part is to be done 100% new then.
Btw: At the moment I am thinking about replacing the UI with another development system, and let the processing part in Xojo. May be it will be in a Web-centric framework then.
Well, there are dozens of threads in the forum talking about that, but the mains source is the documentation, Xojo has allways said, DO NOT OVERLAP CONTROLS (on windows):
Based on that part of the documentation, there is a Blog post that they keep sowhat updated with each change in the framework:
No, it does not make a good job in many areas. But it is the way the Xojo framork is designed so you have to read the documentation, and make the performance tests BEFORE doing the full app.
That could work. If it works in the windows inplementations, it will be a lot better on mac. (And not exaclty a OS problem)
As I said, it can be done in Xojo desktop working wround the Xojo performance problems on Windows, but you should decide if you try with another tools and get a better app. If you take the web road, I think Xojo is not up to the task there
That is what I did. In 2019. And it worked fine with Windows. Btw: These tips are nearly useless because wrong links (now?) and missing references (“see also”) at the Controls- and Container sectons. OK, things like this can happen. But then Xojo changed something and I did not cross check meanwhile. This was clearly my fault. Now I am going to change two things:
It looks promising at the moment - even if there will be hundreds of #If TargetWindows in the code then. At the moment I am struggling with refresh problems - I will keep you informed.
Thanks again for the contribution of your know how in this discussion.
To be fair the links @Ivan_Tellez provided are good (really good actually). However, if some of the links within Xojo’s blog or their documentation are broken then you can report those to Xojo (nothing Ivan can do about those).
You are right, this is true. Sorry for my wording.
They broke a few weeks ago with the change in the documentation, but, you can search the topic Windows ui guidelines in the new documentation site, it is not that difficult. Anyway, it is almost the same as the Design tips I provide earlier.
https://documentation.xojo.com/topics/user_interface/windows_ui_guidelines.html