The term "tankie" was originally used by dissident Marxist–Leninists to describe members of the Communist Party of Great Britain (CPGB) who followed the party line of the Communist Party of the Soviet Union (CPSU). Specifically, it was used to distinguish party members who spoke out in defence of the Soviet use of tanks to suppress the Hungarian Revolution of 1956 and the 1968 Prague Spring, or who more broadly adhered to pro-Soviet positions.
I've never understood why there is any confusion over the word "tankie." It applies to the pro-cop left. If a leftist believes that it's necessary for cops to beat minorities and dissidents into submission for their society to function, they're tankies. If they approach leftism in a way that does not involve state violence against civilians to enforce those ideas, they're not tankies. To me there isn't a lot of gray area.
Tankie doesn't really mean anything to me anymore. Even self-proclaimed tankies often have trouble defining it in a way that is consistent among leftist groups.
Truly. Any moderate support for AES? Immediately labeled a tankie, I've seen Anarchists and even Liberals labeled a tankie. The term only exists to punch left from the Liberal POV, just like "Woke" is used to punch anything left of fascism.
The conversation around "tankies" reminds me heavily of "neolibs" - loosely defined in the minds of the folks discussing them. Basically a catch-all term for your own idea of what a liberal outgroup should be.