Xfinity wifi far slower than wired connection-how to fix?

I have my PC hard wired to to my own modem/router which I use for xfinity internet. I am getting around 371 mbps on a plan that I should get around 400mbps. That's not the issue. Using my two smart tvs and iphone 13 pro max I am getting very slow speeds on wifi. I get 35mbps to my iphone when in same room as the router. Getting under 30mbps to my tvs which are around 30-60 feet away basically one room and 2 rooms away from the PC/router set up. What can I do to increase the speed? I never fully lose connectivity but more times than not I will have things buffering on different tv apps. Hard wiring stuff is out of the question due to the distance and hassle. Would a range extender help me get better wifi signal to those 2 locations if I put it between the router and the furthest TV?