I intend to have a NextCloud instance on multiple servers but these are controlled by a web interface. That means I’m looking for something like a load balancer. The then automatically distributes the users or even edits on both a user. Of course the user should not notice this. Is there such a thing or how can I implement such a thing?
Are you looking for proxies with anycast, proxies with dns load balancing or an HA cluster?
You can also configure a CDN or cache mirrors if your goal is to reduce server load but not run multiple nextcloud instances.
I would recommend researching this independently as it’s outside of the scope of support within this community. If you want a KISS method then nextcloud enterprise (premium) has this built in.
Seems possible if two servers share same storage and use distributed locking with redis. A reverse proxy could distribute user sessions to each server. Mind the php session ids and apache sessions are also stored as files.