Selfhosted

Joplin can be a multi-user solution as well. I use Joplin with Nextcloud. If you don't want to share notes just use Joplin and every user can use the same nextcloud instance, but different user accounts, to save their notes. If you want to share all the notes, all the users can synchronise with the same Nextcloud user. You can make different notebooks for different users. All the users, however, can see and edit notes. Joplin cannot be a solution if you want to share some notes. It is either all, or none.

Logseq can be another solution, with the same technique. However, you can use git to synchronise different databases, where one database is used in shared notes and personal databases for non-shared notes. I host my own Gitea (will soon shift to forgejo) to synchronise my Logseq databases.