I feel like Starbucks burns there coffee. Might be the roast. I'd try there blonde or go for a lighter roast. Cold brew can also be less harsh too. But in my opinion, espresso is king.
Starbucks' lightest roast is darker than the darkest roast you'll find from most specialty coffee roasters. They burn the everloving shit out of their beans
They absolutely do, previous job someone brough in a bag of Starbucks ground coffee, and no matter what I did the burnt taste was always there. I like my coffee dark and strong, but this was just burnt.
Fun fact: Tim's switched to a cheaper bean supplier years ago (when the coffee got obviously shittier, I think it must have been over a decade now) and McDonalds (Canada) actually snapped up the supplier. So McDonalds coffee in Canada is actually the original Tims coffee.
Edit: sauce, this random r*ddit comment from 7 years ago.
As a former frequent Starbucks drinker, they definitely have been burning their coffee. Once in a while, my wife needs her Starbucks so I get a black coffee. And 50% of the time, it's burnt.