Apple Music search is embarrassing! On my Mac often times it doesn’t even pick my search and just shows the “For You” tab contents… 
Apple Books can’t even remember which book you are reading after it gets restarted in the background (on your phone or tablet). The same happens when I restart the app on my Mac… This is a very amateur and sloppy job.
Safari is awfully slow when showing all tabs or opening a new tab. After a lot of reading many people pinpointed the problem at having a lot of bookmarks, which makes it even worse. What kind of a software, in 2021, with the absurd amount of processing power 95% of all computers have, is going to lag that severely on opening a new tab because you have some meager 5K bookmarks or so? 
iOS / iPadOS Photos periodically rearranges my albums and I have to arrange them back.
iOS / iPadOS is taking ages to check and populate new GMail messages (to be fair, it might be Google’s fault here but still, it works much faster on a Mac).
Also lately my iMac Pro has rebooted by itself twice (last 3 weeks or so), which left a very sour taste in my mouth.
As we discussed lately, they are slipping badly.