My computer won't connect with anything at all—bluetooth, wifi, tethering—is there a software fix or is it hardware?

I managed to solve the problem.

1. Here it explains that the question mark on the wifi or ethernet icon can be caused by Ubuntu's "Settings > Privacy > Connectivity Checking". Disable that and the question mark goes away, showing full connectivity.
2. However the internet still didn't work. Hmm. With my Android phone connected via USB-C, and tethering enabled, I turned off the wifi on my phone, so it is only using mobile data. Success! Why doesn't it work via wifi? Still don't know, but at least I have something.
3. Now I can download and install the rtl8818ce driver and enable it in "Software & Updates > Additional Drivers". Wifi on my machine works now.