There isn't enough information to conclude much but if you're failing with a take-home assignment setup, there's a chance that you don't have enough experience

There isn't enough information to conclude much but if you're failing with a take-home assignment setup, there's a chance that you don't have enough experience to find your way through such problems (assuming a mid-career position). So either you can make that up by learning more about that stack and investing more time or just being honest and losing the interview process.