I wouldn't bother with a paid dynamic DNS. Most domain registrars let you change your DNS record with an API call (I know GoDaddy does because I use them.)
Then you just set up a cron job to fetch your IP and then change your DNS record to match. I use a subdomain because my main domain hosts a blog and some other stuff on a VPS, while my jellyfin server is at home.
A good search would be "[registrar name] dynamic DNS script"
I think every 12 hours? I'm not sure. But it doesn't need to be super frequent, unless your IP changes often