Lightsail wordpress admin dashboard show 404 error

Hello.

Were you originally able to access the management page normally?
If you were able to access it normally, could you please share what operations you were doing before the error occurred?
Also, if you check the error logs of the web server, are there any logs output that can help resolve the cause?

In rare cases, a 404 error may occur due to an incorrect WordPress site URL.
https://wordpress.org/support/topic/cannot-access-wp-admin-anymore-2/