Document in "Read-only" mode all the time

Mirek_N, this solved the problem for me:

I figured out how to fix it (per my related question at https://docs.microsoft.com/en-us/answers/questions/748329/sharepoint-files-open-in-read-only-mode.html and Idodero's post above suggesting a variation on this same approach). Seems the account connection can be corrupted, especially if using more than one account, so as with many things in Windows, this can be fixed by removing and re-adding the account. Specifically, in the offending Office app where the document appears as Read Only (this will make the changes to all Office apps), remove BOTH the Connected Services AND the account sign-in. Then re-add just the Connected Service.

Steps:

1. Click on File tab
2. Click on Account in the lower left
3. Under "Connected Services," click Remove next to all of the AD-connected accounts
4. Repeat steps 2-3 for all AD-connected accounts (at least for me, it was OK to leave the personal account)
5. In the Upper right (in the Title Bar), click on the Avatar icon (may just appear as initials) for your User Account
6. Click the 3 dots to the right of each AD-connected account and select "Sign out"
7. Repeat steps 5-6 for all AD-connected accounts (at least for me, it was OK to leave the personal account)
8. Close the Office application

I'm not sure if it's needed, but possibly also remove the Work Account from Windows:

1. Click on Settings
2. Click on Accounts
3. Click on "Access work or school" on the left
4. Select the problem Work account and click on "Disconnect"
5. To be safe or if this process fails otherwise, remove all Work accounts (easy to add back later)

With those done, you have removed the problem service. Now you can add them back safely:

1. Open the Office App
2. Click on File tab
3. Click on Account in the lower left
4. Click on "Add a Service" -> Storage -> One Drive for Business
5. Enter your email address for the AD account for the SharePoint/OneDrive folders you wish to access

This will also add the account to your Account menu, so no need to also add it there. If you selected to allow the account to also manage its settings, then this will also add it as a Work or School account in Windows Settings Accounts.