Tankie's original use was for British communists who supported Soviet military expansion. In the modern sense, it is used to describe communists who are authoritarian-apologists. For example, a communist who romanticizes the Soviet Union or makes excuses for the Uyghur genocide is a tankie. I've also seen it stretched to include militant anti-capitalists, or more commonly, "militant," anti-capitalists who call for violent resistance to capitalism from the safety of a keyboard.
Democratic-Socialists are not tankies. Socialists are not tankies. I don't even think most communists qualify as tankies. Criticizing Democrats does not make you a tankie. Condemning Israel's human rights violations does not make you a tankie. Voting third party doesn't make you a tankie. I see this term used here every day, but never correctly.
I'm what most people would describe as left, and authoritarianism is the antithesis of what I believe in.
Calling every leftist a tankie removes nuance to political discourse and groups people together who don’t believe the same things, whose views are sometimes totally opposed.
It’s worth pushing back on how the meaning of this word is changing. OP is not arguing it should only apply to British communists, only that it should not be used as a cudgel against every leftie.
edit: spelling