With OCC Web there were some problems with some Nextcloud versions, maybe Nextcloud 23 was also some problems. I don’t think we can help you here.
Nextcloud 23 has been EOL for 3 years. Are you really hoping to be able to update Nextcloud 24, 25, 26, 27, 28, 29, 30 at a later date? I don’t think that will work.
It would be better to completely reinstall Nextcloud 30. You have to create the users again. However, you can copy the files back to /data/username/files, for example, and then run occ files:scan --all so that Nextcloud 30 at least recognises the files. However, you will lose all the shares.
Perhaps it would be better to get a Managed Nextcloud instead of hosting Nextcloud on shared OVH itself. Then the hoster will take care of the necessary Nextcloud updates.
For single user you can test e.g. Shadow Drive (https://drive.shadow.tech) also hosted on OVHcloud. You can get 20 GB for free. But the apps and sharing time are restricted. Maybe you get also here a Managed Nextcloud from OVHcloud.