Weird that wifi doesn’t work, maybe it’s 5ghz on iphone and your laptop doesn’t support?

Anyway you could try bluetooth tethering, it could be a bit slower than usb but it’s more convenient, just keeping both in the same room should get good signal. I had no problems on android + linux using blueman. I think mint uses blueberry, dunno if it supports tethering too, but it’s pretty easy to switch from one to the other.