Defer recaptcha script

Despite a good google search, all I can find is how to prevent loading on pages without forms. What I would like, and what Google suggests in Lighthouse, is to add ‘defer’ or ‘async’ to the recaptcha script.

How would I do this?

I can see the loading script (called in recaptcha.php) whicj calls modules/recaptcha/index.js but that file being minified, I can’t see where the code to call the google script from gstatic is – it is this file that is causing Google performance problems. At the moment all I can see is removing the recaptcha integration from contact form 7 but ‘baby, bath water’ is the phrase that springs to mind.