Yes. A 10sp cassette is a mm narrower (counter-intuitively) than an 8sp and 9sp. That spacer means the lockring does not bottom out when tightened (40 Nm - decently not stupidly tight, 6 clicks is my rule of thumb). There will not be a spacer behind the current 8sp cassette.
So we had a go last night.
Got the cassette fitted with no problems, it’s an 11speed hub so we fitted 1mm spacer, all good.
However we have cut the chain too short and it will not shift into big cog/big cog (would never ride like that anyway but it’s annoying) We sized the chain using big/big plus master link as per GCN YouTube guide,but alas it’s too short.
Rest of shifting is perfect…. We are inclined to leave it. But if we wanted to rectify,apart from a new chain what could we do, I’ve never re added links before.
Pics for confirmation of what we have.