This is what I would change:¶
Messenger App - On the left side, you have a list of your most recent messages. On almost any other messenger app, you have an indicator whether the last message was written by you or the other person. In iOS, you can see this clearly based on colour, but you still have the problem. In MacOS, there is absolutely no indication. You have to open the conversation, which makes the last message less useful.
First up, iOS seems to make no sense when leaning from vertical to horizontal. It sets an array in order, 1-through-24, and it resets them. A much easier approach would be to leave the app icons exactly where they are, and just rotate them. It's a lot less jarring, and easier to find. Why this isn't an option 12 versions in, I have no idea. And only 20 on iPad? Really??
The "back" choice to return to the previous application has a ridiculously small target, but it is relatively usable. It's just not the same colour as other tap links, so you have to know that's what it is.
iPads have the "Show Date in Status Bar" option, but iPhones don't. Why not? Just require that the date format be small.
If you pull up from the bottom on iPhone, it's the same as if you pull from the upper right corner of an iPad. Why?
All iDevices should allow a mode you can boot into that accept an HDMI signal. All of those old iPads doing nothing... well, they could be a Raspberry Pi screen, a gaming screen, a second monitor... not something to be thrown away.