To start with, I'll do the two that stick out the most:
1. iOS limits you to 1 timer at a time. On my android phone "Okay google, set a timer for 10 minutes. Okay google, set a timer for 20 minutes" resulted in two timers. iOS will only let you replace the older one. This still bugs me since it changes how I cook a bit.
(1/2)
2. It took me over a year to figure out that I could make my alarm fade in by going through setup in the health app... which now makes a special "sleep" alarm show up in the alarm app, which does fade in. But also has a different ux to set it and can only be set in increments of 5 minutes?
I would not have ever found this special type of alarm that does fade in by default if I hadn't googled this.
The health app changing the options in alarm app feels bonkers.
I'll add another one, since it hit me again today:
If I put the screen to sleep (tapping the power button) and change the volume up or down too near to each other, the volume gets "stuck" going up or down, and either goes to 0 or blasts my ears.