Strength Training Frustrations ?

I’ve been working out with FitnessBlender for a very long time now. I remember having the app (crazy 🫣.) There have been different breaks throughout my fitness journey for different reasons but over this past year I have really, really pushed myself. Recently, I’ve noticed my workouts were getting too easy so I knew that meant I should probably up my weights. I also started FB Fit Round 4 to keep it “spicy.” But I’ve noticed such a decrease in intensity in my workouts, especially lower body. My forearms give out SO easily and I’m just not feeling the same muscle burn out intenseness I have come to really enjoy. Which leads me to believe my form must be incorrect? I just find myself pretty frustrated after most workouts. Has anyone been through this??