Buy a USB-C/Lightning to 3.5mm dongle and leave it permanently attached. Not ideal I know.
But one benefit is that the DAC Apple designed in that dongle is so good that the sound quality far exceeds any phone with a built-in 3.5mm jack.
This is absolutely not true, there are a ton of phones with better DAC/amp combos than the one on the Apple dongle (and even when the dongle is better, it's frequently not better by enough to be audibly different). Unfortunately some of the best analog audio came on phones that were made by LG who threw in the towel last year.
[1]: https://www.audiosciencereview.com/forum/index.php?threads/r...