It’s got a learning curve, but RTL-SDR / RTL_433 (misnomer since it does a wider range of frequencies) options are probably a good place to start with a relatively low entry price (other than time).
Home Assistant RTL_433 as an example.
Now, that being said, if you want a lower learning curve, but a higher price point, a Bond Bridge Pro with Bond Sidekick remotes can be used in direct-RF control mode, or Scene Mode – which allows me to listen for Sidekick remote presses via a computer running a script, and do whatever I want upon said presses.
Just a tiny bit more about these capabilities
Finally, if you have a Harmony remote and something that has the capability to run Hue Emulator / Emulated Hue (I’m a little fuzzy which versions still run on Home Assistant), I believe you could make a fake Hue Hub, then assign Smart Home buttons on the Harmony to fake entities made under that fake Hue Hub – and then have Home Assistant do things upon those fake entities getting an On or Off command from the Harmony.