Finder - windows in Big Sur

I did think of one other thing, resetting NVRAM.

Reset NVRAM or PRAM on your Mac - Apple Support

I can't reproduce it in my Big Sur installs either. You could see if it happens in Safe Mode.

How to use safe mode on your Mac - Apple Support

Are you using multiple desktops or external monitors? There was one other report of similar behavior.

You could create a new user, log into it, and test. I don't know what else you could try other than reinstalling Big Sur.

No, ASC is a user forum. Apple is not here. You can click "Contact Support" on the top right of the pages.

I have this problem too. A little different than shown in the video. I am using an external monitor and my macbook pro. I also do use Spaces (multiple desktops) . In one space I keep two finder windows open with several tabs in each one. Any time i leave that space for other apps, then click on the finder icon in the dock, it returns to the finder space but opens a NEW TAB in whichever window was left active. Very frustrating. Never had this behavior in Catalina or any previous OS. It is very consistent and very frustrating. When I go to the finder I want to find it as I left it. Popping a new tab removes the focus from where it was and forces me to go and click it closed just to restore the view that was there when I left. Looked for any settings in finder prefs that would create this behavior but there was nothing there. All suggestions welcome.

I don't need a video. I understand what you are describing. It doesn't happen for me.

I'm out of ideas. I have Big Sur installed on 4 Macs; iMac Pro, MacBook, MacBook Air and an M1 MacBook Air. None do what you describe. Might be time to ask Apple Support.