I believe that if you send it as a file instead of as a normal image you can send it uncompressed, (Attachements Button > Documents / Files > Select image in fi

I believe that if you send it as a file instead of as a normal image you can send it uncompressed, (Attachements Button > Documents / Files > Select image in file picker, I guess they make this non obvious because people will gobble a ton of space even if 95% they can make do with hyper compressed blobs