As discussed in this archived thread folks who have DNSSEC already enabled through Google Domains are getting a “DNS server responded with NXDOMAIN…Once enabled, click Refresh to see if you can move to the next step” error message at the first stage (“ENABLE DNSSEC”) of registration, sending folks down a rabbit hole to try to fix what’s not broken. The solution is to skip that step and proceed directly to adding the TXT record, but that is not at all obvious and makes the new user experience a lot more blocking than it should be.
I’d suggest that the order of the instructions be flipped, instructing the addition of the TXT record first, and/or fixing whatever bug is causing the error to be reported when checking for DNSSEC.