Challenge according to who? You’re the best judge of your workout intensity. It’s about what you feel. Not about what Miriam does on YouTube.
What felt easy two days ago might feel hard today. Or the other way around. Depending on the calibration of your life’s blistering madness at any given point.
A good intensity for most workouts is somewhere around eight out of ten. Some are going to be less. Very few need to be ten.
“Good” meaning, enough to progress without feeling like a heap of overboiled tagliatelle afterwards.