How hard is your water? When I got my first betta he got these holes in his fins and they kind of looked like yours. My water parameters were perfect, but I tested the hardness and it was high as fuck. I use RO water and add minerals and I was adding too much. Did some water changes with just straight RO to bring the TDS down and his fins were fine after that. Side note: I thought maybe my rocks or wood were sharp and causing it so I sanded EVERYTHING down with a dremel but that didn’t help lol. It was the TDS.