You really shouldn't be gaming while not plugged in anyway. That's the way it is with pretty much any laptop, including those built for gaming. I assume yours has the Max Q 2070 GPU from what I've read on that model. If so, it's definitely gaming capable and will easily play most games at 60 FPS or above on max settings. You have to realize though, such graphics power also draws way more power.
Do you use it mobile a lot? If so, like I said, just leave it at default settings and make sure you're plugged in when you play games. The more you mess with settings to force high performance mode and take it off battery saving mode will only mean the battery will likely run down fast. Your main problem as I suspected though was assuming you could play games on the battery with no problems.
And yes, it's normal behavior. You can't expect a laptop with tons of graphics power to run games on the battery without it either throttling down to integrated graphics, or draining the battery real fast. It's just a fact of portable electronics like it or not. I realize laptops lately are vital, with school coming back and remote learning and all, but if you use it for that, you should prioritize THAT while on battery.