Hey, it definitely doesn’t have to be just a subdomain. You can have a record for example.com point to your VPS’s IP at the same time you have www.example.com, nextcloud.example.com, and jellyfin.example.com. Have as many services and domains as you like and the reverse proxy will direct the traffic to the correct local server based on the domain name.
One way you can do this flexibly is to have two records in your DNS: an A record pointing example.com to your VPS and a CNAME pointing *.example.com to example.com. That way, any subdomain will go to your VPS and you only have to add new services in the reverse proxy.