I use the mac version ( https://krita.org/download/krita-desktop/) for Krita and i accidentally deleted a few default brushes that I really like. I've tried uninstalling and reinstalling already but that didn't work out too well. I looked at many threads about this matter however those were only about the Windows or Linux versions. My resource folder won't open either.

Look for something called 'kis_paintoppresets.blacklist'(it's an xml). Look inside and you'll see the names of deleted default brushes. Delete those entries, save, restart Krita and your default brushes ought to be back.

Krita uses blacklisting to prevent you from accidentally deleting your presets entirely, so they first just get blacklisted from installing, and then you can use edit->resources->cleanup/remove blacklisted files to get truly rid of them.