If i remember correctly there used to be a "Ban Appeal" mod here, does this still needs to be updated or was this on another site ?
Thanks in advance.

Yh there is but you have to manually update it

What parts needs updating, no expert in mybb mods but you sound like as if changing the version number won't be enough

I think you need to change/update hooks and rewrite some parts of code to make it work with the latest version.