They support the use of literal tanks to crush any rebellion or uprising against the authoritarian communist state, and then deny that it happened at all.

The term was coined when the soviets crushed the Hungarian rebellion of 1956 (local communists didn't want to be under soviet rule, soviets sent in tanks) The original tankies supported the soviets

Then there's Tiananmen Square, the CCP crushed protesters with tanks until fire hoses could wash the sludge down into the sewers, Tankies claim it was justified, when they acknowledge that it happened at all.

Tankies deny the ongoing genocide of the Uyghurs. Or claim that china is only detaining "rebels".

And finally, tankies tend to be pro-Russia, even though it stopped pretending to be communist in the 90s. The tankies tend to be anti-Ukraine in this conflict.

Another aspect is the 100% denial of any western media or released intelligence, because it's all evil capitalist propaganda.

Basically these types of Tankies have picked up a history book, seen the overwhelming evil that the western powers have propagated and decided that anyone who stands against the western powers must be good. Which is stupid as fuck.

The world isn't black and white, it's not good vs evil, it's varying shades of greed and evil vs other shades of greed and evil. Tankies tend to not understand this simple truth.