tristankhalil

Did you make a pre-upgrade database backup?

I’m not sure what you mean about this but I backup everything including the database.

Btw, the plugin is now OK. No more error now. And I can search for new plugin.

Looks like it’s still trying to propagate with the new changes.

How outdated? Did you make a pre-upgrade database backup? Trying to carry out a large upgrade (ie more than 2 versions) in a single step carries a serious risk of trashing your database.

Admittingly, yes, around 2 versions. I never thought it would be that risky. Does that mean I need to reinstall WordPress altogether?

Here: https://www.annjones.com