You could just block all cookies and make exceptions to enable them for the few websites that you need to log in.

The only downside is the GDPR warnings keep coming back. I've been making custom CSS and JS injection rules to get rid of GDPR warnings though by removing or hiding them from the DOM -- any Adblock-style plugin to get rid of all of those? If I hide all the GDPR popups with custom CSS, I will have never seen them, and therefore never agreed to them, and if I block cookies they can't track me anyway.

uBlocks "Annoyances" list should cover a lot of cookie and GDPR notifications. If that doesn't go far enough there's also a really great ultra annoyances list that'll unstick and remove just about anything that tries to constantly stick itself on your screen.

https://github.com/yourduskquibbles/webannoyances