I would agree with with many of the issues you have experienced here. Nothing personal, but I am kinda glad, I thought I was going crazy and was the only one having these issues.
Totally agree on the shutdown, etc.
Biggest thing that is broken for me is simple window management. If I have two apps on a desktop, clicking on the the bottom one doesn't raise it to the top. If I open a context menu (for example, right clicking on a link in the browser) the menu opens UNDER the browser.
On my machine, 6 is not ready for prime time. And I have no idea how to categorize things to try and report the bugs. Could be Wayland issues, but I can't figure out how to start a Plasma 6 session in X11 to see if the problems go away. Maybe my window issues are a result of using Activities (which apparently no one else does) but I don't want to shut all that down.
I've decided to (re-)install Kubuntu to go back to 5.27 and hopefully come back when 6 is actually ready.