pages and numbers not syncing with icloud after update

Apparantly an automatic update was rolled out recently, which updated my OS to 13.7. Since, I cannot update any Pages, Numbers and probably Keynote files to a shared iCloud folder. Upon opening such a file a popup says: "Cooperation not possible. If you want to cooperate, use iCloud.com or a newer Mac", which basically means that Apple thinks it is about time I trade-in my 2017 MacBook Pro.

Can I downgrade to an earlier version of Pages, Numbers etc, or even the OS?

I share all my files via iCloud with multiple other users, so cooperation is important!