@dpoggemannthank you, that sure helps a lot!
This means, for a canvas app that allows users to CRUD custom tables and run instant flows from the app, I should set all the custom tables:
Create, Read, Write, Delete columns to "Business Unit", and
Append, Append to, Assign, Share to "None".
In my basic understanding of the matter, "Business Unit" means "Yes", whereas "None" means "No".
BTW: for users to be able to run flows from the app: what tables/columns should be configured?