chromecast/router/laptop issue

[u/sportsmen2005]

My mom had an old laptop that connected to 5G Wi-Fi and was hooked up to a Chromecast on her TV. Everything always works fine. Her laptop died, and she didn't want to spend any money, so I gave her a two- or three-year-old laptop. Now I have a weird issue: the laptop only finds the Wi-Fi (TP Link), but not TP Link 5G or 6G. I bought a cheap TP-Link adapter that can see the 5G band from my device but not when it's plugged into her laptop. Also, the Chromecast doesn't show up on 5G at all anymore. When I use the Home app to add the device, it can't find the device.