I did the same as twobeatsahead two days ago, and can confirm it works.
I thought it was something in my Custom DNS section under the Google domain settings. I wiped all records out and only had the three required for domain verification...and nothing. It turned out it was the records under the Synthetic Records section. (Thank you Chris from SS support for pointing that out).
Chris from Squarespace told me what record needed to be edited, and what it needed to be changed to. The issue is that a Google Workspace synthetic record can't be edited, it needs to be completely deleted (as mentioned above). Yes, it is scary, and your email will be down while you make the changes. I recommend opening a support chat with SS so they give you the edit, copy it, open a support chat with Google, explain what you need done, and paste the change that SS gave you. Google will walk you through every step, as they did with me. As soon as I hit save, they had me check if the domain was verifying on SS, and it was. Instantly, no down time, and email was up. It doesn't take the 48 hours you might see, so don't be scared of that.