UPDATE
Just a quick update on this. After a lot of help from @Jim M I have managed to get my site onto PHP 8.0.
It seems even though all my third party applications and plugins were turned off, PHP 8 still did not like certain ones installed - so I had to remove the offending apps. Unfortunately in order to remove them, I had to switch back to 7.4.
I was hesitant to delete them all at once hoping that it was only one that was causing the issue. So I ended up testing the removal of each app one by one. In the end I had to remove all of them. Here are the third party apps I was forced to remove:
Movies
Forms
Ideas
Raffles System
Links Directory
I am hoping to have updated versions back online as soon as possible. My members really enjoy them.
Hope this is helpful. 😄