not a proxmox user myself, I prefer LXD, but the snap works fine in LXC, see SCUBA’s Nextcloud snap server setup & specs… sure the fail-over redundancy is a bit overkill, but really cool 
its no big deal running the Talk:HPB on the host with Docker right alongside the snap either, provided you use a reverse proxy. see High Performance Backend for Talk on Nextcloud with Docker
same goes for Collabora CODE and Nextcloud office as Docker on the same host, see Install & configure Collabora CODE on Nextcloud with Docker