I’ve had relatively good luck with docker in containers but eventually decided to run docker in VMs as I only semi trust most docker apps and like the added security I get from having it in a full VM in full isolation. Some of the workarounds for docker in LXCs are far from security best practices.

Yes, Alpine maintains Nextcloud in their repos. I mount my NFS share to the Proxmox host (you can mount using the gui and set it to any form of storage you want) then bind mount the share folder to the LXC. I moved from docker in a VM to this LXC with no disruption to my data.

Alpine packages services like Gitea and Nextcloud which Debian does not. This makes keeping up to date alot simpler for myself but that’s personal preference.