Possibly. But just because you replaced the flapper doesn’t mean that it’s not still the problem. I’ve found that the Korky brand is better than the Fluidmaster brand, and have had a brand new flapper still leak.
I can’t remember the brand but the last replacement flapper valve I bought at Home Depot had a stainless steel replacement seat in the package with it. It was a ring with a U cross-section and a tube of silicon goo was also included. The instructions were to shut the water off and drain the toilet tank, then soak up the extra with towels so the outflow hole was well away from water and good and dry. Remove any loose scale or debris from the old seat. Fill the groove in the back of the new seat with goo and squish it over the old old one, then let it cure for an hour. Replace the flapper valve in the usual way.
Worked like a champ and no tank leakage into the bowl since then. Of course, with the stack vent’s location and the way the wind plays over it, I often find the bowl with almost no water in it. I have to crack the flush valve a few moments if I’m doing a #2.