I’ve tried a couple of the tubeless repair kits for fixing tyres in the field.
The weldtite one is great. 6 uses, no failures.
The Panaracer one is pants. 5 uses, 3 failures.
For a hole that size, and given that you’ve already put a tube in (so lost your sealant) I’d put a patch form the inside. I’ve temporarily fixed a sidewall gash with an inner tube patch. You could also try something heftier like a tyre boot.
You would probably also want to use some thread/floss to keep the hole closed and stop the tyre from bulging where it is damaged. If it bulges, it’s going to take more abrasion form rocks, snag on edges and be more likely to get gashed again.