I’ve used Duck DNS and dynv6 in the past and can recommend both.
These bastards at FB Messenger block both of them 
Can’t send any messages with subdomains of theirs.
So it seems I will have to get another domain and connect it by CNAME. But then again, probably the free ones will be blocked as well.
I could ask jendrusk to connect it to a subdomain of openstreetmap.org.pl but I potentially wanted to use it for private stuff too.
For now, I installed DuckDNS on my old soon-to-be-replaced machine. Warnings above apply.
http://ricoelectrico.duckdns.org:31337/QA_map/mismatched_street_names_de.html