You can use local certs with nginx proxy manager as well. You can upload certs via the web ui.

Rather than local certs though, I would recommend buying a domain and using it locally, with https. The problem with the local cert approach outlined in the video, is that importing a root cert opens up a big security hole to MITM attacks. If an attacker gets the root certificate, they can now MITM everything else your browser is accessing. You turn the browser from one of the most secure components of a modern OS, into only as secure as the server hosting the root certificates.

The approach I would prefer, is to buy a domain, and use it locally, using DNS-01 challenges to get letsencrypt signed certificates even from within an internal network. Both Caddy and NPM have support for DNS-01 challenges.