There is no specific rule against using this however it is highly adviced you don't use it.
We handle this the same way we handle the use of other simular cases such as vr mods/tools.
There are many different mods, tools or apps etc. that allow for such things. There is often controversy over...
You can also just use forge 1.16.3 and put the 1.16.2 optifine in the mods folder. all i did when upgrading to 1.16.3 was installing forge 1.16.3 but i kept my 1.16.2 mods and that worked fine. So if you for some reason don't want to use optifine preview versions because they might contain bugs...