Not really feasible in a lot of cases without giving up things the business absolutely wants. I work on an e-commerce site for a large company. Marketing wants to track all clicks and user inputs and get heat maps to improve the conversion based on their findings. They want to know where their users come from, where they go to see if their campaigns work. They also want google maps integration to find retail stores. They want users who come back 2 days later to retain their shopping cart and their preferences even without a login in case they checkout without an account. They want dynamic A/B testing based on user behaviour and they don’t want to/can’t reinvent all these solutions so they go buy them and the devs get to integrate them - whether they like it or not and some things simply make it so that you need to store some data on the client and communicate it on the client in some way while not being completely anonymous.

So cookie banner it is and to be sure you don’t get sued you buy that elsewhere.

> Notify on signup for everyone else.

You don't need notifications for purely functional cookies. If you have a Nextcloud instance that only uses a cookie to remember your user identity throughout a login session, no notifications are required. If you also feed the value of the Nextcloud cookie into a tracking system, that's when a notification is required. And only then.