It is certainly something that would be great to have. Unfortunately, it is not that easy, to run two instances is no problem, the question is what do you do after both went out of sync? What if a file has been changed on both setups, what if some database ids are the same but with different entries?
You have a similar problem with the synchronization of the clients but there the server wins.
For larger setups, there were some deployment recommendations in the documentation:
https://docs.nextcloud.com/server/11/admin_manual/installation/deployment_recommendations.html
But there you have more than just 2 servers and it is not to sync over two locations and often you still have a single point of failure.
There was some announcement last year or so to have multiple locations. I found a repository (GitHub - nextcloud/globalsiteselector: The Nextcloud Portal allows you to run multiple small Nextcloud instances and redirect users to the right server) but no recent news. And since such stuff is very interesting for enterprise customers, there are probably less public information available.