Sticky Notes Icon on taskbar is not combined

Here in January 2021 with the same issue. The newest update got rid of a lot of good features, including this and customizing the task bar colour, for seemingly no apparent reason. It's incredibly frustrating. This is why I put off updates as long as possible. Windows, if it ain't broke, DON'T FIX IT.

This is exactly my problem. I came to the same conclusion as you about the cause. Unless lots of people complain, MS won't bother fixing it.

Sadly and unfortunately even they get a lot of complaints they will likely not change it. They make these kinds of stupid decisions/changes that only create annoyances or unusability from something that was working great and they ignore any complaints or requests to revert. There're litanies of forum strings of users begging for them to return a form or function that was removed/negatively changed that go unanswered.  My system was just updated and I'm here a year and a half later because this horrible issue is still in effect. Stick Notes is now unusable for me. I don't want to combine ALL of my taskbar icons and even if I did I STILL have to click on every single note, one at a time, to view them.

Additionally if i go into taskbar settings and enable Use Small Taskbar Buttons then ALL screens now show non-stacked sticky note icon and labels on the taskbar.

THIS is why i disable Windows 10 updates and block via my 3rd party firewall, any windows services from calling home. Every time an update rolls out it breaks something. I've spent way too many hours fixing something after a FORCED update when i've got better things to do. I've hated the forced update system since the beginning of Win10. I am still amazed why there's still no big revolt. Microsoft is so authoritarian no more so that with Windows 10. 

Anyway this time i had accidentally left my 3rd party firewall OFF overnight and during a reboot. Next morning. Updates were awaiting. I have 3 screens and most, not all, of my notes reside on the left screen. Yet after the m$ forced update i found all my notes on the main center screen AND the task bar labels all separated (not stacked like before). So so so so effing annoying.

Strangely though, when i look at display settings the left screen turns out to be the primary screen, with the center and right screen being screens 2 and 3. Now curiously any sticky notes i drag to the primary screen stack normal with labels on the the side as normal. However, any sticky notes i drag to the secondary screens (screens 2 and 3) do not stack and are shown on the taskbar separately aka not stacked. Dragging a sticky note from a secondary screen to the primary screen stacks properly only on the primary screen.

I don't really have time for this.