Are you looking for this? https://anvil.works/blog/multi-user-apps
Multi-tenant/single-DB is a pretty common and straightforward pattern with a lot of support in Anvil (eg restricted views, as described in the video).
I'm also currently working on a multi-part video series, showing the creation of a SaaS product, from scratch to monetisation. Sign up for our mailing list, and watch this space :D