Here is the link to salesforce Permissionset object. ctrl+f required permission name.
userType Field has these value options (not updateable):
Standard: user license. This user type also includes Salesforce Platform and Salesforce Platform One user licenses. Label is Standard.
PowerPartner: User whose access is limited because they’re a partner and typically access the application through a partner portalor Experience Cloud site. Label is ...
Have a look at "Delegated Administration": https://help.salesforce.com/htviewsolution?id=000004559
Here you can specify which custom objects the user should be allowed to manage.
There is also the permission "View Setup and Configuration" permission which can be assigned via a permission set. This will enable them to access (view only) ...