"Grit my teeth" - Means clench your teeth/jaw, as in to endure pain or something "Grind my teeth" - It means basically moving your teeth while they are clenched, some people do it while they sleep and grinding them down, which is bad

Literally/physically they are essentially the same action, though grinding is often involuntary (possibly done while sleeping.) "Grit my teeth" is sometimes use as an expression meaning endure difficulty to get something done. EX: "Despite my frustration with the University, I decided to grit my teeth and finish my dissertation." "Grind my teeth" is more likely to be an expression of frustration. EX> "The government inaction on climate change make me grind me teeth."

Grit my teeth: This means clinching your teeth,people do this when they’re angry or unhappy about something. Grinding my teeth: This is basically when someone rubs their teeth against each other. It makes a grinding noise. Hope this helps. Good luck 👍🏾