Comment by qbasic_forever

Tor/onion hidden services are under-appreciated here and a good fit for potentially replacing ngrok: https://community.torproject.org/onion-services/setup/

You need to run a tor daemon on the server side and then a tor browser or tor on the client side, but other than that there is no other setup or intermediary service/server necessary. This solves a lot of pain that many ngrok alternatives still require you to run (or pay for using) some central hub server, have a public IP & DNS, etc.