Google Domains is closing down and the domains are being transferred to Squarespace, see https://support.google.com/domains/answer/13689670

One of the things that won't carry across is auto-verification of the domains in Search Console (if the domain and search console are using the same Google account, they could be automatically added to Search Console).

However, as part of the migration, all your DNS settings will be transferred, so to be covered, you can add DNS as a validation method now.

How to Do That

Log in to search console, and go to Settings on the left hand Menu, then click Ownership Verification:
Click on 'Additional verification methods', we're going to use DNS here, but if you have a url-prefix property, you'll see other methods, you can follow them instead of the rest of this guide if you'd rather
Click on the Copy button:
In https://domains.google.com/ navigate to the domain, and click on it, then select DNS.If Default Name Servers are active, follow along, if not ask whoever manages your DNS how to add a TXT record and pick up on step 7
Click Manage custom records, then on the blue "Create new record" link that appears.
Leave the first field (Host name) empty, For Type, Choose TXT, TTL can stay at 3600 and in data, paste the field copied from search console in step 3, then the Blue Save Button
1. Go back to the Search Console tab and click the Verify Button, and you're done!
  This might fail the first couple of times as DNS can take some time to propagate, so come back later and try again. (it could technically take up to 48 hours, but it's usually faster)
  
  Still Stuck?
  Open a thread, with details of the domain you're trying to verify, you can do so by clicking this link