Getting Permissions problems on Mail Attachments, Books and documents in other applications

Since the last Big Sur security update (or at least I think that is when the problem started), I've had a host of problems with accessing documents from various applications. For example, I can no longer open attachments directly from Mail, although I can save the attachment and then open it. Some books I can no longer open (I get a message about permissions error and told to view the information in Finder). Similarly, in some other applications that include attachments or documents (e.g. Tap Forms 5) I find I can no longer directly open the document, but I can save out the document to open it. This is very inconvenient and I don't understand what has happened. This applies both on my MacBook Pro which is relatively old and cannot be updated beyond Big Sur and my iMac (last Intel version) which I could update but I've kept on Big Sur to be consistent with my MBP. As far as I can tell by looking at the documents in the Finder, the permissions are all correct.