How to restrict users to only select/read/etc Customers where they are the account manager

I assume this is a pretty common use case, but I cannot find how to do this

Also, how can I assign a user to only see customers assigned to a group of users

Go to role permission manager and give the permission you wanted for customer doctype for role account manager.

This just allows the user to read all Customers

What worked was to make a user permission like this

user@ > Allow [User] > user@

This enabled the customer due to the field [Account Manager] which is linked to [User]

But to allow a hiearchy like I wanted I proceded like this

Create a [Salesperson], for each [User]

Add each user permission

user@ > Allow [Salesperson] > Their salesperson ID

Then add [Salesperson] as a linked field in the [Customer] table

Managers go like this

user@ > Allow [Salesperson] > Parent salesperson ID

Try user permission then .