I came to your topic WiFi setup and troubleshooting "WiFi setup and troubleshooting" while trying to troubleshoot a Raspberry Pi 4B which could connect to VNC/SSH while connected to the router by ethernet, but could not do that over WiFi, despite being able to access the internet.
This section of the post helped me
'If you do see your WiFi's SSID, a couple of lines above that you should see a line that starts with "Quality...". It looks something like this:
Quality=43/70 Signal level=-67 dBm
This shows numbers relating to the quality of the connection and the signal strength. These numbers can be useful when troubleshooting a noisy or weak signal (repositioning the Pi in relation to the Wifi access point can often help improve the signal). [We could use some examples of what is considered good or bad numbers here]"
I want to add my numbers:
The network on which the problem occurred had: "quality=20/70 Signal level=-82 dBm"
The network which fixed the problem had "70/70 signal level -29 dBm"
This is just my experience, but I wanted to add it there because the post specifically asked the community for examples of good or bad numbers. Either because I'm a new user, or the vintage of the post, I can't make the edit myself, so I figured I'd start a new thread. That thread is a very helpful resource and it fixed a problem I've been troubleshooting for 3.5 hours now.
Hope my data is helpful!