I have a 3s I have Android 10 just flashed no nonsense via IMG and everything works and good battery. Pixel experience reloaded it's called.
That's pretty much what I did. As had been mentioned, follow the instructions and you can't really go wrong. I'd recommend using one of the better supported ROMs with a larger following. I went with Pixel Experience for that reason but the official one isn't supported on Mi6 anymore, but like I said earlier everything works fine so I'm happy (but always tempted to try something new).
no worries, i think what most novices like us need learn is to follow the instructions. there's been times when I had spent a whole day fixing my mistakes for not following the proper instructions lol
Thanks, that's pretty much what I'd requested, a useful website (y)
Read xda forums for the specific device and check YouTube. Like most things, it's better to dive in and learn in the process imo