Google font added to header.php not being optimized

Whwn I manually add a google font to header.php it doesn’t get optimized, it remains as a render blocking resource – the Google fonts that my theme uses are no longer render blocking.

I tried enqueing the font instead in functions.php but there seems to be a very long FOUT – whereas the fonts used in the theme I don’t get a FOUT.

Wondering if there is a correct way to manually add a Google font to ensure it gets optimized by the plugin?