That is not really possible because it would require a constant check-in and subscribe feature for merging “local” changes made by others. The blocker of this is in the clients themselves, not on the server.
Yes. OnlyOffice, Collabora Online and so on. These has clients for devices as well as through a browser. No, they will not look and feel like the LibreOffice suite, but those supports collaboration with “live” update of documents.
However, why not just use a browser and use the native Nextcloud Office? In order for collaboration to work you will need to be “online” anyway, hence using your browser is as viable as it gets? Then you can use LibreOffice as an offline client.
Collabora Online - or Collabora - has both mobile device apps as well as clients for windows and Linux. However, the GUI is far from the experience you get with M365 and LibreOffice. When you get used to how they work and how you access the “tools” menues, it has nearly all the same as those two others, but the getting-used to is definately a topic. Those clients do have collaboration natively.