Noncompatible with WiFi Modem/Router?

Try rebooting the modem/router. Make sure the router's WiFi frequency settings are set to "Auto" so it will do its best to find an unused channel free of neighboring networks and interference. See if your WiFi channels are overlapping any of your neighbor's WiFi signals. Make sure the router's firmware is up to date. If setting the routers WiFi channels to "Auto" does not work, then you can try to manually set them to a channel not currently being used by your neighbors. Keep in mind this unused channel may later be used by a neighbor so the "Auto" setting is preferred once you are done troubleshooting.

Reboot the Apple laptops. Try Safe Boot on the Apple laptops as this will load minimal drivers, remove some temp & cache files and it will not load any Startup Items or Login Items which should minimize software issues. While in Safe Boot, you may see the screen flash or flicker due to the very basic video driver being used.

Option click on the WiFi icon on the menu bar of your Macs and see how the Macs are connecting and check the signal and noise levels. The ideal signal level should be somewhere around -36db to -55db with the noise level around -90db.

Hi Asking4myDad,

Thanks for coming to Apple Support Communities for help today. It sounds like your father's MacBook Air and Pro won't connect to a new Netgear router.

The easiest way to troubleshoot this would be isolating the issue by seeing if the Mac computers will connect to other Wi-Fi routers. It sounds like they recently did with the Spectrum router, but you may want to try again.

You can also check out this page: Check for Wi-Fi issues using your Mac and even run Apple Diagnostics: How to use Apple Diagnostics on your Mac.

Being sure all Mac computers are updated would help as well: How to update the software on your Mac.

If they connect to other Wi-Fi networks just fine, you should contact Netgear. It may be that your new router requires a software or firmware update.

Have a great day!