App and tab visibility on profiles and permission sets
Key Takeaway
The profile sets the defaults, and permission sets add more access on top. Neither one can deny access, so when a user's tab settings differ, the most permissive setting applies.
App and tab visibility settings control which apps a user can select in the Lightning Platform app menu and which object tabs they see in an app's navigation bar, the App Launcher, or the All Tabs page. Both profiles and permission sets hold these settings.
Profiles and permission sets
Every user has exactly one profile but can have many permission sets. Salesforce recommends using the profile for default settings, such as the default app, and using permission sets to grant additional access.