Years ago, back when TD Bank's regular credit card (and debit, for that matter) was FTF, I used it in Canada at a restaurant. The server at a restaurant must have chosen USD by default, as I had not been given a choice or informed at all. I noticed it when we left the restaurant and I did a chargeback. I got the difference between DCC and regular rate back after a few weeks, so not sure if they did an actual chargeback or just refunded me the difference.

FWIW, looks like Walmart does not do DCC, as I had used my Polish card there. So, so far only Walgreens. I will test out a few more big chains in the next few weeks.