Literally on the way to replying to this, I encountered this graphical UI bug in Safari:
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What you're supposed to see here to the right of where it says CP (a google doc) are two more tabs. One I opened to reply to you, the other I opened as a second attempt. Above are my Favorites Bar bookmarks to Headfi Forums and my Synology surveillance cameras. There should be two active page tabs in that blank space. If I minimize and then bring the window back, they finally appear. I have seen this since 26.0. For Apple in their flagship browser, thats insane.
I do lots of work with file sharing over SMB. My network is rock solid. The number of times Finder has some kind of fit over a connected server's mount status, how it responds (or simply doesn't) to volume ejection commands (back through Sequoia) is embarrassing.
If you have multiple spaces and your Calendar app is on one space and you double click a.ics file, you aren't brought to the calendar where a new window has popped up to ask you what calendar you want to pin the event to, and if you really meant to add this even to your calendar. Instead, everything in your active space becomes unresponsive until you figure out that you have to manually skip over to the space with the calendar app open.
Messages does not reliably tell you a message was delivered. It often just leaves it blank on iMessage. Did it deliver or didn't it? Why no readout? Has been like this for many generations of macOS even after Messages got its little overhaul. They dont even reliably change the version number on the Apple Apps anymore.
In the Music app, sometimes the search just stops working and you have to quit the app and reopen it.
Contacts app is design wise the most cluster****ed overlap of UI of nearly any app on the Mac.
In the Finder, find a video file, right click it, go to Services and select Encode Video File. Then try to uncheck the box that says "same as source file" for the save location. Notice you both cannot uncheck the ticker box but you also cannot see the words because they overlap.
If you want more, listen to Gruber's last two episodes of the Talk Show with John Gruber.
Im really not here to be a jerk and say Im a better more Mac-ier user than you are and if you are really using all aspects of the OS I dont know how anybody can say things are fine. There is not a single pundit (ATP.fm, Gruber, Snell, etc) who says anything other than this. John Siracusa who wrote macOS reviews for like a decade for ArsTechnica wont even upgrade because it's so rough and riddled with bugs. Sorry. Facts.