Why can’t i come back to older working version of php after ugrade with error log on php 7.2 and 7.3

The problem was nd_mysqli php modules not activated for 7.2-7.3 but that still doesn’t explain why restore didn’t work once activated it worked but had some webmaster fix it for me. Maybe caching but i kept flushing caches.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)