MacBook won’t connect to internet after trying to install HP printer

Depending on the printer, it may have been necessary for you to connect to that printer using a peer-to-peer (ad hoc) network created by that printer for the sole purpose of configuring it. If that's the case you may need to reconnect to the wireless network you had been using prior to configuring the printer. To do that start with Connect to the internet with your Mac - Apple Support. Be sure you are connecting to the correct network and are using the correct password.

My provider is saying my router doesn’t even support WPA2.

That's really odd because all recent routers support WPA2. I suspect whoever you spoke to did not understand the problem. Try simply restarting the router — unplug its power cord, wait a moment or two, plug it back in again and wait for it to restart.