Once again replying to me but killing Taniks is seen as completing raid and is enough to complete gauntlets. So get Taniks check point and push through it with some blueberries (guide video before encounter is also helpful).

So. I got check point for Taniks and tried but didn't succeed. And then read this: Destiny 2 Update 3.2.1 Fixed an issue where players could damage Taniks before starting the final encounter. Sad news for solo players who thought they could get armor upgraded easily.