FLIRC is your friend! It's a USB IR receiver that you can train with literally any IR remote you have. Once you set it up (and it does take a little elbow grease to train it), it just works.

Keep an eye out for the new Steam controller. It can interact via gyro, touchpad, and traditional controller input methods.

I believe Kodi supports IR remote controls.

I use LibreELEC on a mini-PC for my home TV. LibreELEC is a Linux distribution that runs Kodi and is pretty good for a media centre straight out of the box. I use a Rii Mini K25 remote (with a dongle) to control it: https://www.amazon.com.au/dp/B06XHF7DNQ

The downside is I can't control the TV itself with this, but this can be sorted out with a USB IR receiver (like this: https://amzn.asia/d/0hvzkP93), LIRC (https://lirc.org/) or something similar, *and a universal remote. On my to-do list lol

I have a DHCP reservation for the TV itself and it's blackholed on my network. The only reason it's connected at all is so I can monitor what it tries to do.

Edit: Also need a universal remote for the IR solution so it can talk to the PC IR receiver and the TV IR receiver separately.

My HTPC is running Bazzite and boots into Steam big picture mode. I watch media using Kodi and control everything using a Sofabatton remote.

This setup is almost as seemless as when I was using an Nvidia Shield and a Logitech Harmony remote.

The keyboard and controller are not needed, except for gaming.

The only negative I've found, is that I've not yet worked out a way to power on the PC from the remote.