What is the best percentage to charge my MacBook Air M1 to???

Let the MacOS manage the power/charging system. Plug in the computer when needed or when convenient to do so. Leaving it plugged in will not damage your computer or battery. You do not need to micromanage the system.

Hi,

One exception. See Store it half-charged when you store it long term.

Batteries - Maximizing Performance - Apple

If you are using it at your desk, leave it connected to the charge circuit. As Bob says above, there is absolutely nothing to be gained by trying to micromanage the charge process.