Cannot copy and paste multiple images into iMessage on BIG SUR

Upon upgrading to BIG SUR I can no longer copy and paste, via a folder or the desktop or any location on the computer, more than one file/image at a time into iMessages. When you do, they appear like this --

-- and then cannot be opened by either myself or the contact they were sent to. You can however drag multiple files still but this is not convenient at all times.

Same goes with PDFs, however you cannot copy and paste a PDF at all, even one at a time into iMessage, it must be dragged. This was never the case prior to BIG SUR. I also have issues with sending images entirely to a contact via SMS on the computer, as SMS is linked via my iPhone and prior to BIG SUR I could send images to SMS contacts and now cannot at all -- they fail each time and say "not delivered".

Additionally, images cannot be dragged from imessages when clicking the (i) on the top right of a message as they used to be able to. And, images that should appear do not - it just says "Shared links, photos, and more will be shown once Messages finishes indexing" consistently for weeks.