Lockring tight, no space for a spacer but the 3 largest cogs which are on a carrier work loose, help

You’ve probably got a notched freehub which prevents the whole cluster being preloaded, or the 11T is on wrong which would also prevent the whole cluster being preloaded.

Other possibility is that it’s a road 11 spd freehub like a Hope, and needs a spacer behind the cassette.

Yeah, I felt some play in my cassette last week. Tightening it did nothing. upon removal of the cassette, the freehub is notched big time.

Sometimes light touch with a file might give it a bit more life.

If it is a hope (or any other) alloy freehub, check it for cracks – mine did this – the crack was tiny but caused what is happening to you