Get an iPhone when you need one. There’ll always be something better in the future.
For some, myself included, it's hard to say when it's time for a new phone.
Going from my 5 to a 6s Plus felt significant for me. Going from 6s Plus to XR felt like a solid upgrade, but not quite as necessary. Admittedly, if I wanted the most impact, I should have opted for the XS Max, but that's another story.
This time around, I'll opt for the top-of-the-line model. That way, it'll feel like a true upgrade. Of course, not everyone needs the very best model. The XR still had most of the benefits of the XS models, but there are definitely differences in almost every category.
In the end, it's impossible for us to advise the OP on what phone to get because we know nothing about them, their use cases, their current phone or what would excite them about a new phone.
For me, screen quality and size increase is exciting. Other bells and whistles are kind of a bonus for the most part. The camera isn't that big of a deal, but I don't want a crappy camera. The performance of my XR is still just fine. I don't imagine iOS 15 changing that, since Apple is still going to support the same phones as last year.
Kind of excited to see how the smaller notch looks. ProMotion is cool, and it's nice to finally be coming to iPhone. I've also been curious about MagSafe. Seems like a cool feature, and it's nice that it's stronger this year supposedly.
Lots to consider.