Unable to slice Sprite Sheets in TileVania

[lvskiprof]

I am using Unity 2021.3.0f1 here, since it was the first LTS release.

In lecture73 on Slicing Sprite Sheets it has has go into the Sprite Editor to do this (I have done this on the previous version of this course), but the option to do slicing is greyed out:

That is making it a little hard to proceed any further.

[lvskiprof]

I think I see the problem. I had to set Sprite Mode to Multiple. When I click on the provided ones they are shown as Single. Now I get the option to Slice and it looks like it will work.