There are several threads open on this; you can see them commencing since the day 11.6.6 came out. I have posted in every one of those and there is no "workaround" except closing Preview every time you want to open an attachment. then clicking Open for another attachment, which will open that attachment, then quitting Preview and going through the same routine over and over again for each attachment. The same holds true for .jpg's, Word, Excel attached to Outlook, to Mail ...
I can assure you that giving full disc permissions for Outlook does not remedy the issue.
Please submit a bug report to Apple ... this problem is not going to get fixed until they know it is affecting many folks. Perhaps the best way to submit the report is to use your Feedback Assistant.