UE5-MAIN branch builds fine but cant open some projects with assertion error

This happens to me too when building the development editor.
It may happen because the check code is faulty.
you can try DO_CHECK 0 in the UE_BUILD_DEVELOPMENT section of:-
Engine\Source\Runtime\Core\Public\Misc\Build.h

or remove the line

check(IsInGameThread());
Engine\Source\Runtime\Core\Private\HAL\ConsoleManager.cpp : Line 556

Then rebuild the editor.
I am not a programmer, so it may break something else.