I agree with Rob. You should be doing both and the resistance bands are a great tool (just use them carefully with proper anchor and grip).
The knee pain on the bike could be one of two things: 1) an injury or 2) you don’t have the seat set right. If it is an injury, you should go see an orthopedic doctor and potentially a physical therapist. The pain you feel now while on the bike could eventually affect you during other activities (walking, dancing). If it isn’t an injury, I could talk you through how to set the seat height.
With any fatigue issue, it is important to know whether it is physical, nutritional, or hormonal. If you have some idea about the cause, we can dive deeper into strategies to address. In the meantime, just push to the line but not over it. I’m pretty sure you’ve found that line while dancing. Flirt with that line during your cardio sessions, just stay on the south side of it.