We have previously tried this workaround and didn’t have any joy, since there is a unique parameter ID “registrationcode” added to it. And it was no longer added when we copied the registration URL a generic automation email / workflow.
A Contact could get to the registration page, but the email field remains blank (instead of having their email prefilled) and inaccessible / greyed out (can’t fill it out). And they had nowhere to go from there. So we ended up sending an email series that refers them back to the original registration email (or to contact us to get this resent)
@SteveHTM have you got this live and working?