I think it’s the muscle memory aspect others have mentioned in the topic that is the first and foremost jarring aspect.
Following on from that I’m not enjoying the ramming everything into the one bottom row to solve the minimal upper aspirations, it feels like a case of swapping one extreme for the other here, yes minimalism is a challenge.
I actually think the bottom also has visual alignment/ tangent issues, and is visually annoying, and creating an active visual pull, there is a lot going on here, it’s resting around only 50-75% final solution, thus it looks unfinished.
However one very specific point that is easily actionable.
I don’t know why in the top left of the composer pop-up is used a share type icon, for the “Reply as/to…” button.
It’s already established and used as the “upload” button in the bottom menu, a bad UI decision here, how this occurred, well I don’t know but that’s a no no, it’s also visually lowercase, this is not reading or doing what it’s suppose to in my book.
For lack of anything, I suggest revert to the original icon (or functional equivalent) or remove it totally, even the later would be an improvement.
That icon should not be there.
Note: The above points are all desktop based derived feedback.