In my MacOS Passwords I have ±3400 entries. A roughly 341KB CSV. Searching in that list in the preference panel or Keychain app is dog-slow on my M1 Pro Studio or on my M3 MacBook Air. How??
This is the obvious low effort, low complexity solution. Of course you could make it fast, but that would take time and effort for a feature most people won't notice.
The new Passwords is a joke. UX errors all over the place, modal based view with a toggle to start editing. If you need to enter a password in another area of System Preferences, you need to back out of the auth flow, switch to Passwords and copy the credentials over to a temporary file.