Yeah, whenever I see something like that, my first thought is, “Doesn’t work like other apps on your OS, so will be a pain to get used to, will have weird inconsistencies, and won’t integrate properly with OS features that come standard with all other apps you run.

I know. In theory, custom UI doesn't necessarily mean to have such freedom to "change" what UI's rules of the OS has been established. It should sound more like, I don't use your way of rendering stuff.

To me that’s a turnoff, you might get an IDE where the speed is faster, but updates and fixes will be slow to come because the team could not get over NIH.

From what I've heard from 10x users I know, the dev is extremely responsive and bug fixes are often published within hours of being reported

I mean custom as in "I wrote it myself". It's not based on a slow and bloated UI framework. Hopefully it's fairly standard from a Windows point of view though.

If you want to know more, I have lots of dev videos on my youtube channel. https://www.youtube.com/@puredevsoftware

retained or immediate mode?

retained