IR blaster for smartphones. I still have one on mine and I can use it for tons of stuff, not just as a TV remote.
I even worked for a company who made lots of IR based products (taps/faucets, accessibility stuff) and it was amazing how many people had to buy the dedicated remotes for these products for extra money.
When I asked them if their phone has an IR blaster, so they could just download a free app and use it instead. "I have an iPhone" was the most common answer.
There are small and cheap USB-C IR dongles around nowadays - generally USB-C has been a blessing for making additional hardware features available on smartphones.
My current phone does have IR - though I'm not really using it much since most of the existing Android software for that is horrible (broken, ad-infested, requires account and access to everything, ..), and I have too many open projects to start another one for writing my own software for that.
I agree the software is bad. All my phones bought after nexus 4 was made by Xiaomi. They give option to unlock bootloader and flash custom rom.
Not all the phones get official lineage os support, but almost all snapdragon versions get custom rom support.
I gave my Redmi Note 4 to my mom, which is 6 years old and running latest OS with recent security patches. None of the other OEMs were supported upto this period (just give exception to Samsung Galaxy 2).
I do have a Xiaomi phone and as I mentioned I am actively using the IR blaster, but the majority of regular users will not even think about checking the specs when buying new tech.
They will just go for the latest iPhone or the current trending android bestseller.