All i want is when i go to ns.example.com it show me only the login for ns.example.com and there is no way to add an exclusion to the “default match detection”
As explained in the help article, you can set the match detection to “Host” on all your logins. They will only be suggested when the host fully matches (subdomain and port included) the page you’re on.
Another Lastpass password manager had the ability to specify which mapping to perform for the example.com domain. In Bitwarden Manager, the mapping happens either GLOBALLY or at the individual password / host / URL level. It is not comfortable. This could be tolerated if it were possible to change the settings of ALL hosts for the domain example.com. And so you have to either manually edit each host, or do export to JSON / edit in a text editor / import again. But here, too, there is a pitfall - when importing, all imported data is duplicated, and if all elements can be deleted all at once, then each folder has to be deleted separately.