Same here. Mullvad’s awful policy that essentially limits you to having their client installed on 5 machines was also a deal breaker for me. Sure I could have fucked around with managing keys/connections myself, but why bother? I emailed their support about how inconvenient it was, and they told me I was free to pound sand or pay them for another subscription to enjoy the convenience of having their client installed on more devices.
Proton has been great since I switched, and I see no reason to use Mullvad these days.
I switched to a paid domain in the last few months and regret not doing it sooner - it just works, and it’s nice knowing that I won’t have to reconfigure all my stuff to point at a different domain name again in the future. Price was maybe $15/year on porkbun - very much worth it imo.
I’ve also used freedns in the past and had no complaints about them, except that I think wildcard subdomains are limited to paid supporters (very cheap though) and at the time my SWAG docker image maybe didn’t support them? It’s been a while. The service was great though. Never had problems like I did with duckdns.