The article covers this a little bit, but I thought I'd share my email response from Google when I asked them "how can I prevent Squarespace from receiving any of my data?" They responded with:
Based on the summary you have shared, I understand that you need help with your general inquiry about the Google Domains transition to Squarespace. To answer this, if you will be transferring your domains out of Google, all of the data will also be removed. This means that once the transition between Squarespace and Google happens, your data will also be removed.
I responded to this and basically said, that wording is ambiguous. Will my data be removed before or after the transition? They replied:
I'm sorry for the confusion. To be clear, Squarespace will not receive any of your Google Domains data. Only the active domain names, excluding the domain names that have been deleted or transferred out, will be affected by the data shift to Squarespace.
So if I trust their word, it means, if I've already transferred out my domains (which I have), Squarespace shouldn't receive any of my customer information, or even have a record of who I am. Hopefully that's true.