My lad’s tyres once kept puncturing when we were in France, despite what I thought was a through sweep for thorns. It seems he had run over some bloody French vegetation that injected about a million tiny hair sized thorns all the way through his Minions, which I had to sit and remove using a pair of tweezers.
Mark where on the tyre you’re getting the punctures from, then turn it inside out, stretch the rubber as much as you can and drag a soft cloth or your fingers across the area. You may even have to search inch by square inch, in good light with a magnifying glass. As I discovered, they don’t have to be big or particularly visible to puncture.
Then go tubeless.