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.