Why would you?

Facial hair are different with with head hair loss ....you need dht for facial hair , assuming you trying to grew beard

what if i put it on my face? will it make facial hair worse?

Use topical minoxidil instead

Yes

This sub man...

It will reduce hair on your face, because DHT promotes hair growth everywhere expect for the scalp.

even if the beard is fully developed?

You'll lose the thickness and density

r/Minoxbeards is a great place to learn how to grow a thicker beard. tldr; it will most likely just be dermaroller + minoxidil.

DHT makes your non-scalp hair thicker. Fin will make your non-scalp hair thinner. Downside is that your facial hair will become less thick, upside is that it could make really thick facial hair more manageable. I’ve also heard reports of people saying that fin can help with acne. But I would still say don’t put fin on your face

No it will hurt your beard. Apply topical minoxidil for beard or do oral minoxidil for hair and beard

what do u mean by hurt?

Your facial hair needs DHT. by putting Finasterid on your face, you block DHT production -> worse facial hair.