I've done a fair bit of trying over the years; based on your comment I retried today I still cannot find it under Settings -> Safari -> Default Browser App.

To be fair though, I did find it on my wife's iPhone, though under Chrome (she does not have it under Safari (or General either, where I would've expected it)). Still don't have it anywhere on my iPhone. I'll try to see if that's because she's ahead of me on OS updates or some other reason.

Thx!