If this iframe loads a resource running on your WordPress instance, then yes.
But, in most cases, the answer will be: No.
TL;DR it's technically impossible to detect Google Fonts inside an iframe loading an external resource. If you can't or don't want to remove it, block it behind a cookie banner (like Real Cookie Banner) and ask for consent before loading the iframe.
Most embedded iframes out there are provided to your by 3rd parties as an easy way to insert their application on your site, e.g.
- Google Maps widgets,
- Recaptcha,
- Youtube videos,
- Support Chat widgets,
- etc.
Iframes are essentially loading (external) webpages inside (or as part of) another webpage. The external resource is loaded to be looking like it's a part of your webpage.
Logically, since OMGF (Pro) is installed on your server, it can only inspect resources on your server for Google Fonts.
GDPR implications of using Embedded Iframes.
Just like Google Fonts, there are GDPR implications using embedded 3rd party scripts, i.e. Youtube Video's (or Google Maps or Recaptcha) on your website. That's why it'd be a good idea to reconsider using them altogether.
In a recent ruling in Germany, a website owner was fined simply for using Google Fonts, because the IP address is shared with Google's servers while downloading the files. The same goes for embedded Youtube videos, or any other embedded element (iframe) -- which is hosted (and maintained by) a company in the US.
If you absolute need to keep using them, at least block them using a cookie banner (like Real Cookie Banner) and ask for consent first.