Optus 5g modem bad for gaming?

Before I bought my first gaming PC I got on Optus 5g modem plan with uncapped speed, not an NBN. With the ethernet cable connected to the computer (I keep it connected), I get a download speed of 150-200 mbps. But when I play call of duty online it lags and has high latency. Is it from the modem/internet option or do I have to fix computer settings. If it's computer settings what do I need to fix? thanks.