Collections button can now be hidden from the Edge toolbar

It was added in the previous Edge canary update but at the time of posting this, it's from Version 81.0.392.0 (Official build) canary (64-bit)

still not available on Dev channel but should be added in the next major update for Dev.

p.s this has been requested multiple times on the forum. previously the only option to hide it was to completely disable Collections feature using the flag.