I've done that with Lunar (https://lunar.fyi https://lunar.fyi) Lunar 3 was free and open source, then a very high effort upgrade had to happen because the M1

I've done that with Lunar (https://lunar.fyi https://lunar.fyi) Lunar 3 was free and open source, then a very high effort upgrade had to happen because the M1 CPU needed different low level logic for controlling monitors, so I made Lunar 4 paid. I still keep Lunar 3 as a free download right on the front page, and its source code is untouched in the lunar3 branch (https://github.com/alin23/Lunar/tree/lunar3 https://github.com/alin23/Lunar/tree/lunar3) Most people were happy to pay and support me for the new app, but inevitably there were some very rude messages because some users felt entitled to getting the upgrades free forever. I think it's a perfectly reasonable thing to do, it's your work and your time and you should ask to be compensated for it if you need the money.