This is an existing bug and needs improvement.

When searching, Proton Pass currently perform the search field by field. So let's say I got a Google account, with username: protonuser@gmail.com. If I search with the keyword "Google protonuser", there will be NO RESULT. It will show up only if I search "Protonuser" or "Google".

So, the current logic only consider content of each field separately.

My suggestion: Consider Item by Item.

If I search "Google Proton", the login item with item name "Google" and username "protonuser@gmail.com" should show up.