I thought this as well back in 2019 regarding the animation stutter that appeared on the XS, XS Max and XR. It still hasn't been fixed, I can observe it clearly and easily on my XR and I observed that exact same stutter in the iPhone 12 Pro Max at the store.
My advice for anyone who is bothered by this is to activate Reduce Motion and forget about it. Apple won't fix it. Back in 2018 this gained traction because the premium models were stuttering and there were articles about it. So Apple can't be unaware of the issue, they know it's there, it's just that a) they don't know how to fix it or b) they know how to fix it, but won't because it probably requires more effort than they want to put in.
The thing that tells me they absolutely won't fix this is the fact I was able to see this in the iPhone 12 Pro Max almost immediately at the store. If the latest and greatest model has this, what hopes does my XR have?
Reduce Motion on, good job Apple.
Oh and a disclaimer: what I said applies to the well-known animation stutter / frame rate drop that has been present since 2018. This may or may not be the same thing as the stutter that brings up the app switcher. What I wrote applies in general to the stutters seen in iOS these days because it's been here too long for me to think it will get fixed. As a side note, my dad's iPhone 6 doesn't have animation stutters. When I saw this, I quickly stopped hoping for a fix.