Yesterday, Apple released macOS Big Sur 11.6.7 for compatible machines, with a fix for a bug in the Mail app. macOS Big Sur is still being used by those computers that cannot be upgraded to macOS Monterey.

The bug that this addresses is released to the official Mail app and other third party ones such as Microsoft Outlook and they were unable to to open attachments if the app required to open the file is already running.

‌‌‌‌‌‌‌macOS Big Sur‌‌‌‌‌‌ 11.6.7 is available now and can be accessed by going to System Preferences > Software Update.