apple7819 wrote:
When I forward the email with attachment in Apple Mail on MacOS Monterey, email is sent as separately ATT000x htm including my signature also.
who has solutions for this problem?
That's just the way email works. When you officially "forward" a message, it totally scrambled the format.
What you can do instead is select the original message and choose "Send Again" from the Message menu. This will create a new e-mail with the original message unscrambled. You can send it to someone else, and even add your own comments. But trying to do a "forward" will "quote" the original message, and scramble the internal content.
Your signature is just a bunch of attachments anyway. I recommend that your signature be strictly plain text to avoid this kinds of problems.