This snap makes the following channels available:

Channel Description
stable The latest stable release of Nextcloud
candidate Release candidates of the snap (not Nextcloud)
beta Trunk of development in the snap
edge Daily build of upstream Nextcloud's master branch
12/stable The latest v12 stable release of Nextcloud
12/edge Daily build of upstream Nextcloud's stable12 branch
11/stable The latest v11 stable release of Nextcloud
11/edge Daily build of upstream Nextcloud's stable11 branch

You can install any of these with:

$ sudo snap install nextcloud --channel=<channel>

Or, if you already have the snap installed, you can switch channels with:

$ sudo snap refresh nextcloud --channel=<channel>