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.

https://docs.erpnext.com/docs/user/manual/en/role-based-permissions

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 .

https://docs.erpnext.com/docs/user/manual/en/user-permissions