SharePoint Limitations of OneDrive App for External SharePoint Guests

Hello everyone,

I am part of an organization and have created two SharePoint sites:

• one site for all members
• one site only for the board

External guests have been added to both sites.

Problem:
Several of these guests would like to use the OneDrive app (desktop or mobile) to access the shared content. This is where I am stuck.

Situation in detail:

• Some guests do not have a Microsoft account, others have created one themselves
• The SharePoint sites and documents are shared correctly, and access works via the browser
• In the OneDrive app, however, guests do not see any content
• Nothing appears under “Shared”
• The SharePoint sites are not visible

Questions:

• How are external guests supposed to see SharePoint documents in the OneDrive app?
• Do guests have to have a Microsoft account, or is an email-invited guest sufficient?
• Is there an official or recommended approach for enabling guests to use OneDrive/SharePoint meaningfully via the app?
• Or is the OneDrive app simply not intended for external guests?
• Additional question:
  Is it officially supported or expected that guests can only access SharePoint content via a web browser (on PC and mobile) and not via the OneDrive app at all?

I find a lot of contradictory information on this topic, and it has cost me quite a bit of nerves by now.

Thank you very much for any explanation or best practice.

Best regards,
Nina