Welcome, cubsfanbudman and @All, to Apple Support Communities!
I see we have another case where the actual problem is in the way Microsoft Outlook disallows you, the user, to perform bulk operations on attachments, such as images (photos), when Outlook renders (displays) the attachments inline (what all too many refer to as “embedded” into the email).
Please do note, no matter how any given email client (such as Outlook) may choose to render (display) an email, all files (images or whatever) are sent as attachments to the email: this is a very old aspect of the Internet email protocols!
Yes. There was some change in either the way Apple Mail defaults in the format used for authoring emails, or in choosing a newer version of the Simple Mail Transfer Protocol (SMTP) used (or both), which, apparently, has triggered Outlook to change the way it renders (displays) an email.
However, that does not negate the fact that if Microsoft Outlook would allow you, the user, the right to perform bulk attachment operations, regardless of the way Outlook may choose to render (display) an email, this would have never been an issue.
You may certainly provide Feedback to Apple, requesting that they allow you to choose the default formatting of authored emails, so you may choose plain-text as your default.
Unfortunately, there is no guarantee that this will actually solve the problem, since the problem is the way Microsoft Outlook behaves, which Apple has no control over.
(Note: I would not expect Apple to abandon updating to the use of a newer Internet protocol; especially not just because Microsoft hasn’t chosen to update, yet.)
What is guaranteed to solve your problem, however, is to get Microsoft to set Outlook to allow you, the user, the right to perform bulk attachment operations, regardless how Outlook may choose to render any given email!