Hi there,
I had the very same problem.
So, I solved it by uninstalling all the php7.4 related packages with a
apt remove php7.4*
And then a
apt install php7.0-zip
BUT ! Now, my nextcloud has an issue that must be related to the uninstall / reinstall process… And it looks that I’m the only one having it so maybe you won’t have any issue by removing php7.4.
Good luck