HDHomerun is the commercial solution that is relatively painless assuming you have something that can run a client that supports it

Open source, you probably want to look at tvheadend and a USB DVB-T tuner (hauppauge still make decent ones I believe) attached as the next most straightforward option, it can take a little bit to get set up but it’s pretty seamless once it is. Same caveat about clients

For a good while, Plex was the only game in town that did the job well, and they put the transcoding feature behind the paywall.

Given it wasn’t that expensive for a lifetime pass a number of years ago (I remember it was cheaper than a game anyway) and they still seemed relatively user-centric at the time, many people like me felt like they were supporting developers building something that was useful to us.

I still run my Plex server since it’s not really costing me not to, but I’ve been running Jellyfin too for a little while and it more or less can do the same job these days