Hello, @Kuronuma,
Welcome to the Microsoft Q&A platform!
Based on your description, I understand that you want to know if it is normal for recipients to be unable to access or open emails and attachments sent via OME encryption.
By default, attachments in encrypted emails remain protected when downloaded because the protection is embedded out in the file itself. If you want them to be able to download attachments in unencrypted form, you can finish this by using the following command in PowerShell.
For a more detailed description of the configuration, you can browse to https://techcommunity.microsoft.com/t5/microsoft-security-and/admin-control-for-attachments-now-available-in-office-365/ba-p/204007.
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Thank you for your support and understanding.
Best,
Alex Zhang