Maybe one counter indication of tribalism is how often you disagree with your "tribe". I'm fairly left leaning too, but I also find myself disagreeing with a lot of left leaning policies or talking points. Maybe that's a good sign.
It's only a good sign if they're able to speak out, and aren't terrified of expressing their dissent in public.
Both the left and the right seem captured by a small minority of radicals, using social media echo chambers/purity spirals to shut down often-quite-reasonable disagreement. And we're clearly past the point at which we can just ignore 'social media politics', given how much it seems to have led to the current state of things in the US.
At the risk of sounding pessimistic, and as someone who also identifies himself as leftist: If the end result is voting between black/white binary choices, and that act of voting is itself one of the most important self-expression, does the fact that I disagree with them in a few points matter?
Arguing with leftists all the time is the sure sign that you're a leftist.
(seriously, this is a significant asymmetry between the two that has been there for at least a century. There isn't one lockstep leftism, there's thousands of micro factions arguing about most things)