I've already got Nextcloud up and working at foo.ddns.net - using subdomains like "nc.foo.ddns.net" is easier (single line change, literally) than moving it to foo.ddns.net/nc, which requires picking apart the config file with a fine tooth comb as near as I can tell.

From the docs I have grokked so far, you can put each subdomain in its own config file, completely separate from the other files, and they won't conflict with each other.

Edited to add - one of the things I loathe about being self-taught through experimentation and just randomly stumbling on to things is that I don't always know the proper terminology, have no idea where to look for things, and have this fear deep down inside that I'm leaving my pants around my ankles.