I’m still looking myself, but Corvus OS is recommended for performance and gaming. There are a lot out there and depending on what you want to use it for some will be more suited. Here’s a link I found a while back that lists a few good ones :) https://techviral.net/best-custom-rom-for-rooted-android/
Here’s a few! :)
It’s generally recommended that you put a lighter weight OS onto the phone. Many are available depending on what you want to do and work much better on older devices than android (which updates tend to get heavy and demand more power which unfortunately slows old devices).
I’m planning to do this for a couple old devices and then repurpose them with other uses
A lot of people seem to use apps, one called ‘Remote System Monitor’ looks good, and then connect a charging cable to the pc to keep it charged.
Personally I’d love if there is a way to do this not involving phone apps, but instead reducing the old phones capabilities to just a screen and having the pc recognise and use it as one. That could lead to some interesting possibilities.