adjust line spacing in Apple Mail

In a revised update to my previous post, If you enter the text of your Mail body in LibreOffice Writer (e.g. 7.3.1) first; select that text and adjust the line spacing to the preferred value, you can then copy/paste into Apple Mail's compose window. The desired line-spacing remains. That 2x line-spacing in my example was sent through a GMail account to Apple Mail and the received line-spacing was preserved.

In LIbreOffice Writer:

and Apple Mail on Big Sur 11.6.5 upon receipt of the sent email:

FWIW, Microsoft Outlook has adjustable line spacing.

Line spacing is something to expect from a word processing application which Apple Mail is not. Thus, you cannot set line spacing in the compose window, nor can you control how the recipient's email client displays your sent email.