Is there a free app that will help me visualize / find out which devices in my WiFi network are using the most bandwidth and potentially diagnose other network issues that might be slowing down my internet?

I have 1Gbps internet, and speed tests usually show 350-400mbps on most of the devices, but lately, I am barely getting 10mbps on WiFi.

The wired tests are still coming under <1gbps, so something is definitely up with the WiFi / local network.

I've rebooted the router etc and while it sometimes works, it doesn't work most of the time.

I'd like to figure out what's going on and hopefully, there are some great tools I could use to help diagnose the problem.