Yes I just did, in a private window, and all I needed to do was complete a captcha. But even if your IP is on their naughty list, you can delete that data once

Yes I just did, in a private window, and all I needed to do was complete a captcha. But even if your IP is on their naughty list, you can delete that data once you have registered, and I would be very surprised if Proton secretly kept it after you delete it.