For me it’s the “tap to change volume” on my Galaxy Buds Pro. Such a great feature that saves touches for other functions.
Unless I’m trying to eat while wearing them, especially crunchy stuff, which causes the volume to go haywire (and only on the right, volume up, side).
So I switch to a pair of USB-C Buds when it’s Doritos time.
Popup view windows: I love them but sometimes the apps don’t scale properly and you have to adjust it, the Labs Setting Allow Multiwindow for all apps randomly disables);
Bixby: It has great functionality across the phone, apps and ecosystem (appliances and TVs included) but it’s slow and doesn’t pickup what I say correctly;
Taskbar on Tablets and Foldables, if you keep it enabled it sometimes overlaps part of the apps. I would’ve preferred something like the iPad’s or the Pixel Tablet’s version.