OneNote: Can't sign in with a microsoft account.... :-(

On my business laptop (Windows 10 Enterprise / 20H2) we are using Office 365. One of the applications is OneNote which I also use on my mobile using a private Microsoft account. With that I often take notes (which get saved to OneDrive) while on the go and I want to access these also from my Business Laptop.

When I try to access that data (using the OneDrive URL "https://onedrive.live.com/view.aspx?resid=...&id=documents") and in OneNote select to login via a different account I am first asked for my email address and - after entering that - I get an error box stating:

Can't sign in with a microsoft account.

This program is blocked by group policy
For more information, contact your system administrator.
0x800704ec

I asked our system admin and he says he did not - at least not consciously - block that. He also has no objections that I access my private notes with our office laptops. Furthermore we are all (local) admins on our respective machines, so I have the ability to change group policies and registry settings if necessary.

I thus searched for the above error message and meanwhile I tried all the suggested remedies that I found but that darn error still remains! :-(

What I tried so far:

Allow Microsoft account via Local Group Policy Editor:
With gpedit.msc under Computer Configuration > Windows Settings > Security Settings > Local Polices > Security Options I declared the group policy Accounts: Block Microsoft accounts as This policy is disabled..

Allow Microsoft account
With the Registry Editor under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System I have set the key NoConnectedUser as 0

Allowed Office online features by setting UseOnlineContent to 2:

[HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Internet]
"UseOnlineContent"=dword:00000002

[HKEY_CURRENT_USER\Software\Policies\Microsoft\office\16.0\common\internet]
"UseOnlineContent"=dword:00000002

Enabled SignInOptions for Office to allow Microsoft Account as well as Org ID:

[HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\SignIn]
"SignInOptions"=dword:00000000

[HKEY_CURRENT_USER\Software\Policies\Microsoft\office\16.0\common\signin]
"SignInOptions"=dword:00000000

But none of these setting did the trick so far! What else or what additional setting is there that might prevent access for OneNote to OneDrive using a Microsoft account?

For the benefit of anyone stumbling over this thread:

THIS finally did the trick for me:
[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\MicrosoftAccount]
"DisableUserAuth"=dword:00000000