Intel iMac (Tahoe) iMessage not sending JPEG files

I have an Intel based iMac running Tahoe 26.2. I am unable to send .jpeg or .jpg files via iMessage. I can send .webp files. I have no problem sending messages. This problem exists when sent to iPhones or other brands.

I have signed out of Messages and signed in again. I have deleted Library/Message .db files. I have deleted Library cache files. My date & Time are correct. I have no firewall or security programs. My Wi-Fi is running great. I have signed out of iCloud and back in again. I have shut down my machine several times. I wiped my disk, then installed Tahoe 26.2 again, then restored the disk from three days ago from a Time Machine backup.

I was on the phone with Apple twice today. Three hours this morning and two hours this afternoon.

Short of making my Mac into a boat anchor, any suggestions????