WordPress Error Message: Please create your maintenance page in the plug in settings

Hello.

A file called ".maintenance" may have been created in the WordPress directory, so try connecting to Lightsail via SSH and deleting it.
The following questions may be relevant.
https://wordpress.org/support/topic/workaround-when-you-cant-access-maintenance/

The problem is probably on the WordPress side, not Lightsail, so I think it would be best to ask your question in the WordPress forum below.
https://wordpress.com/forums/