I can't even create a new project. Adding a TButton doesn't add StdCtrls to my units. Manually adding it I can compile and run.
Somehow the component-registration (for example which unit has TButton is screwed up).
Do you also have buster-backports? (that'can be added to /etc/apt/sources.list) That's what I have and may be different from yours.. Since the new video back end this may be a possible cause in the OS.
Mmm, I wonder what package could be using this problem in trunk.
I downloaded everything via svn.
No backport in sources.list
deb http://raspbian.raspberrypi.org/raspbian/ buster main contrib non-free rpi
I did need to use apt update once because apt-get update gave me an error for InRelease (I had a slightly older Buster).
I might try a new Buster distro tomorrow.
But I can't imagine something like that screwing up the config-file for components and not anything else.