There is no correlation in being waterproof and not having a headphone jack. Several phones have both

Samsung has had waterproof headphone jacks for years. My LG v35 has a quite nice "Quad DAC" and a waterproof headphone jack. It's absurd to think that Apple has eleventy billion dollars but can't design a waterproof headphone jack.

I would wash my old Moto G under a tap whenever it looked a bit dirty. It had a jack. Plenty of phones that have jacks are waterproof.

Plenty of IP68 phones have headphone jacks.

Had mine in my short pockets while wet wading and the damn camera flooded and died. I’m less than thrilled with apples waterproofing, headphone jack or no.