A legacy Nextcloud install (from before NixOS 26.11) may be installed.
After nextcloud33 is installed successfully, you can safely upgrade
to 34. The latest version available is Nextcloud34.
Please note that Nextcloud doesn't support upgrades across multiple major versions
(i.e. an upgrade from 16 is possible to 17, but not 16 to 18).
The package can be upgraded by explicitly declaring the service-option
`services.nextcloud.package`.