what is the latest version of Apple Mail

Further to the OP's question. While the Catalina Mail app is v13.4, when I look at the mail folder itself, the mail database is in a folder named V7. I have always understood this to be the version of the mail database. Is that the case? (In Monterey the Mail app is v16 and the mail database folder is V9.)

This is just out of curiosity.

For Catalina which is where you posted, it's 13.4.

Sorry. No idea.