Yes, that should be able to log in that way, but ideally you want to renew the certificate so you can be sure the connection is secure.
Are you able to access the command line on your gateway? You can either plug in a monitor and keyboard or enable SSH in developer settings.
The default username is “pi” and the default password is “raspberry”, but if you enable SSH you will be asked to change the default password.
If you are able to access the command line you can try manually renewing the TLS certificate following the documentation for certbot here User Guide — Certbot 4.0.0 documentation
Something like:
$ sudo certbot renew
Please let us know if this works, and be sure to keep a record of any errors you encounter.
Thanks
Ben