This is all a bit of a “storm in a teacup”. The only time you have to be GDPR compliant is if you collect, store or process information that uniquely identifies the site visitor. In the case of Google Fonts, you are not doing any of those things. However, if it can be proven that Google are collecting, storing and processing such information from your website users, it is they who would be in breach of the regulations.
My own lawyers spelt it out to me in words of one syllable - if you don’t collect store or process such information, you have nothing to worry about. The fact is that the authorities in Europe are not going to bring legal action against the millions of website owners who use google fonts in their websites. Furthermore, there are no legal precedents to suggest that such legal actions could be taken.
If you really wanted to be pedantic about this issue, you should have a welcome page on your website that states that:
By using this website you specifically agree that certain information about your browsing habits may, inadvertently, be passed to Google. Facebook, Pinterest, Linkedin, or the plethora of other third-party websites that we may link to or, who may provide content to make this site work, either now or in the future. Furthermore, we accept no responsibility for any third party tracking codes that may be implanted on your computer by third parties during your endeavour to find this site, including, but not limited to, search engines belonging to Google, Yahoo, MSN, Bing or any others that may appear in the future. All we are saying is that THIS website will not collect, process or distribute to others any information that may personally identify you without your explicit consent. If you do not agree with this, please bugger-off and go somewhere else.
Now, that isn’t rocket science is it?
What you should be concerned about is forms. All you need to do is put an UNCHECKED checkbox on your forms which states that the site visitor agrees to receive a response to their enquiry, or be added to a mailing list or whatever the form relates to. If you do that, you’re covered. Why make the issue a bigger problem than it needs to be?