To protect your own communication with the internet against sniffing by other on the same local network you can use a VPN, i.e. the typical VPN for private use which starts the VPN connection at the local system and has the VPN exit somewhere on the internet, outside of the reach of the other users of the same router and of your ISP.
Protecting yourself ...
The wifi access point is probably recognizing your android device's MAC address, which normally remains constant, even throughout power-cycles.
If you want the wifi access point to 'believe you are a new user', you may be able to temporarily change your MAC address. See https://www.techjunkie.com/change-mac-address-android/ for more info.