I typically like to keep the registration of the domain itself in the customer's own registrar account (even if I have to set it up for them). I provide them with that information (or they provide it to me, if they have already registered it).

Then depending on the registrar, there may be features that help to facilitate this type of management. Porkbun, for example, has "subaccounts" and also "authorized users" where you can then set yourself up to be able to admin those domains on behalf of your client. Godaddy, as another example, has a feature called "Delegate Access", where you can set yourself up under your client's account to be able to make changes, perform renewals, etc. on their behalf.

I would imagine that other registrars might have similar features.