Considering that it isn't the default and it is only available on Windows 10 (and that only since 2015) i think that it is very safe to say that for all intents and purposes "anything compiled with MinGW links against MSVCRT.DLL" is valid and will be for a long time.

Though even if MinGW switched to UCRT tomorrow, it would still leave a ton of executables since 1998 (or whenever it started using it) relying on MSVCRT.DLL (which AFAIK is included by default in Windows since Windows 98 so it has a slightly wider support range than UCRT :-P).