The ability to run execve() on files within an application's home directory will be removed in target API > 28.
Here is the issue on Google bug tracker:
https://issuetracker.google.com/issues/128554619
As expected it is yet another "working-as-intended", furthermore, as commented in the issue,

Relying on exec() may be problematic in future Android versions.

This seems to completely break Termux in a long-term, as all its packages contain executables.