For instance (this is just sequoia, but same for ios) searching for "improve" finds:
"improve assistive voice features" (I turned it off)
and diagnostic & usage data with: "improve siri & dictation" (I turned it off)
but under spotlight, it doesn't find "help apple improve search" (I turned that off too)
Not sure what went wrong for you, these results seem pretty much on point.
The other day “login” didn’t produce Login Items. But I wouldn’t be surprised if you tried it right now and it worked fine.