in your odoo instance configuration file use the configuration parametter:

list_db = False

This will disable the database manager. link and url access (web/database/manager#action=database_manager)

1.To hide the database manager, set list_db = False in the configuration file. 

2.To define the database to be used, set dbfilter = my_db in the same file

Use this to resolve the issue. Clean and secure login: hide the Manage Databases link on the Odoo login page and throws up 404 error if user tries to access web/database/manager. Works even when list_db = True, allowing modules like OCA's auto_backup to operate normally while keeping the login UI tidy.

Hide Manage Databases Link

The below video shows how it hide the databases even we access the link:

https://www.youtube.com/watch?v=HTixATyjR7g

http://www.numberspeaks.com/2020/06/03/disable-database-manager-access-in-odoo/