I ran 20psi in Hans D’s at Coulags and nipped my bead/sidewall exactly like this. I hardly felt it and it was my own fault for leaving the house with such a low pressure. I normally run about 23 24psi-ish on the climbs over there but I thought I’d go a bit lower to prevent pinging off everything in sight.
It could happen on the first off-road corner on the first ride. It could also happen a few months down the road. It’s tough luck. Order a new tyre and bin that one.
Or you could sew it with fishing line and smear Aquasure on both sides before running it tubeless with no leaks. Mine sealed fine with Stans after carefully trimming it at the rim side of the bead. If you’re a skinflint,that is :O)