If you need to share XQ-encrypted content externally and you’re getting this error, you have 2 options
Share XQ-encrypted content with non-XQ Users (Recommended)
If your email recipients are non-XQ users, offloading to OneDrive will need to be set up for XQ Secure Communications. In this case, XQ requires SharePoint link sharing to be set to “Anyone” on the site on which the data is saved. You can configure this as a global setting and then set independent sharing settings for each SharePoint Site.
Share XQ-encrypted content only with XQ Users
XQ-encrypted content can always be decrypted by using the Outlook Add-in or the Chrome Extension. This means that onboarded users will always be able to read your emails, even without offloading.
For folks outside of your organization, you can ask your email recipients to create a free XQ account by logging into the Outlook Add-in or the Chrome Extension. Reading XQ encrypted messages is free, as is installing the extension. They will get up to 5 encrypted messages per month, ensuring they can communicate effectively with you.