I believe it is pretty straightforward since it is in their App Store. https://apps.umbrel.com/app/nextcloud Unless you’re talking about (perhaps) doing secure remote access to your home server?
Yeah, remote access would be ideal 😅
I would very strongly recommend checking out Tailscale. https://community.umbrel.com/t/how-to-use-tailscale-with-umbrel/6782 It is one of the easiest ways to have a secure connection to your home servers, and you won’t have to punch a hole in your NAT at home. Going to tag @Ava in here to double check I’m not giving bad advice.