I expect there is more than one cause for the hanging instances that various people in this thread are afflicted by.
So whilst Teams was the problem in my case, it may not solve the problem for others.
For those who are getting hanging instances, first check if Teams is running.
Go to the notifications area in the taskbar, right click the Teams icon (if present) and click Quit Teams. The icon will disappear
Now open an Access database then close and Quit Access. Do you still get an instance of Access left in background process?
If yes, then Teams isn't the problem in your case so stop reading here!
If no, then Teams is responsible, so read on.
Teams and PowerShell open in startup when I reboot - even when I remove them from startup, they return.
That may not matter but if you don't want it to happen, you can prevent Teams loading at startup in several ways:
1. Windows Settings | Apps | Startup - toggle the slider for Teams to Off
No idea if PowerShell is an issue but probably there will be a similar entry for that
2. Open Teams - click the ellipsis ( . . .) at the top right and click Settings | General and untick Auto-start Teams
That screenshot also shows the unexpected option that was the problem for me
In the latest version of Teams 26005.213.4315.4117, the fourth option under General was enabled (not by me)
In my case that was hooked into my Office apps and preventing them closing cleanly
Untick
Register the new Teams as the chat app for Microsoft 365.
Then close all Office apps. From now on, you shouldn't see any instances of Access (or other Office apps remaining in Task Manager after closing.
NOTE: If you only see the top two options, you may need to change the Language and regional format settings lower down under General, close and restart Teams.
One more thing that is worth checking whilst Settings is open
Click
Files and links and set Word, PowerPoint and Excel file to open in the Browser
(NOT Teams)
Hope that helps at least some of you to fix this issue