SuperTuxKart has come a long way and is very well done. I haven't tried the online multiplayer, but it looks pretty good. I was really impressed that my Driving Force Pro racing wheel worked out of the box. Now I just need to fix the pedals which were designed rather poorly. Fortunately they can be improved with a couple of new potentiometers and some spring steel.
I wrote a small go app[0] which is invoked every 15 minutes and updates the DNS through the cloudflare API. Its very specific for my use case and ISP but works well.
Cool! There's also certbot[0] and lego[1] which can do ACME-DNS with a range of providers beside CF. You could also do tls-alpn, which allows you to do do the challenger encrypted on another port. Sounds like DNS works fine for you, but it's primarily worth considering for those issuing certs for non-public names that shouldn't be broadcasted via public DNS.
SuperTuxKart is truly cross-platform and even has an online mode.
[0] https://www.supertux.org/ [1] https://supertuxkart.net/Main_Page