I always give some bs emails in those authentication forms. Mainly because as a client who tries to connect, I do not have internet access, so I cannot verify my email before they give me the access. And when they gave me access, there is no power in the world to make me do that 🤷
I found a script for bypassing captive portals on Linux back in the day...
The full functionality of how it works escapes me at the moment, but essentially it searches the network for a host that possibly already connected through the captive portal and spoofs their MAC address.
This isn't the one I originally found, but its the same principal and a Kali tool, so it may be considered more secure than the original bash script I copied back in the day:
I used to use an android app that shared log ins for public Wi-Fi even with a password to connwct. It was great as it automated the log in screen too, so was usually seamless.