BUG #19537: Authentication failed regardless of typing exactly my password set from sudo passwd postgres

The following bug has been logged on the website:

Bug reference: 19537
Logged by: JOSHUA CABANILLAS
Email address: joshcabara22(at)gmail(dot)com
PostgreSQL version: 18.4
Operating system: Ubuntu 26.04 LTS
Description:

Hey, I'm using pg Admin 9.16 and have Ubuntu 26.04 LTS running as my OS.
So I tried to reinstall from scratch everything, just to see if this would
work. However, after reinstalling postgresql postgresql-contrib and pg Admin
from scratch step-by-step, and set my password and typed it exactly on the
pg Admin Register Server dialog it threw me the following error:

Unable to connect to server:

connection failed: connection to server at "127.0.0.1", port 5432 failed:
FATAL: password authentication failed for user "postgres"
connection to server at "127.0.0.1", port 5432 failed: FATAL: password
authentication failed for user "postgres"

So I just gave up on trying to fix it for my own and followed through this
forum to submit it as a bug report.
Any guidance for fixing this error will be appreciated.
Cheers.