This is an excerpt from an older variant of the Cessna 172, but it should still be close to how the newer version should be leaned (would be nice if Asobo provided us with some manuals, mind??).
Now the above would be a great thing to show you if the piston aircraft in this sim were realistic, modelled correctly and not underpowered (which they are not).
So despite what I’ve pasted above, you’d probably be better off following a more rudimentary method to leaning a piston aircaft, such as below.
At altitude, set cruise power.
Lean by reducing the mixture gradually until the engine runs a little rough. You may see a slight increase in rpm before the engine starts to roughen.
Slowly enrich the mixture until the engine smooths out. This is what’s known as a “best economy” setting.
If you need to climb, enrich the mixture before adding power if at or above 75-percent power, then lean again at your new altitude.