When you invite external users to a LiveTiles site, you may be faced with a registration page. To avoid this experience please follow one of two possible solutions:
- Create a new SharePoint group> grant it Read permission to the subsite called LiveTiles Design>add external user to that group.
- Reverse MS change so that Everyone will now include external users. This method will require: SPO Admin rights and MS SharePoint Online PowerShell. See this article: https://docs.microsoft.com/en-us/office365/troubleshoot/access-management/grant-everyone-claim-to-external-users