I remember watching a Ukrainian aircraft tracking across Europe several weeks ago before it went dark several hundred miles from their borders.
There might well be operational reasons why tankers and the like haven’t gone dark to show Russia they are there and are active and in the cases of tankers on racetracks to say we are here and although you cannot see them we are not alone, or maybe they are but either way you cannot see that fact.
The internet can be good and bad, I should imagine Ukraine is scouring it for films uploaded by their countrymen showing Russian movements in theatre so they can work out who and what is where.