10 to 11 speed cassette – is this spacer needed?

Hi Bikewrench,

I'd like to switch the 10 speed cassette on a wheel to a 11 speed.

I've noticed that the whole stack of gears doesn't fit when the spacer pictured (first thing to go on the hub) is on the hub, but when I remove it, the whole stack including the spacer between the single cogs fits perfect.

Is this just another spacer when using 10 gears or would I need another/longer freehub to run 11 gears?

Thanks! 🙏