want to use Airport Extreme only for Time Capsule backups via Ethernet

was using Airport Extreme as router and as backup device for Time Machine.

Not sure how you did this, since the AirPort Extreme is a router only. It has no hard drive on board. It is possible to attach a USB drive to the AirPort Extreme and back up that way, so that might be what you were thinking.

Or, you might have been thinking about an AirPort Time Capsule.....which is in effect an AirPort Extreme with a built in hard drive.

Perhaps you can clarify.

In either case, the standard setup is to connect your AirPort Extreme or AirPort Time Capsule to the Netgear router using an Ethernet cable if you want to back up using Time Machine.

It might actually be possible to connect the AirPort the way that you ask, but it is a complicated task to set this up...and it has not worked all that well when I have tried it.

If you connect the AirPort to your Netgear router, you will then have the option of connecting an additional Ethernet cable from your Mac to the AirPort, or using the Netgear wireless to back up using Time Machine.

If you don't want to set up things this way, then it would be best to sell the AirPort and connect a simple USB drive directly to your Mac for Time Machine backups. Backups will be simpler, faster, and more reliable this way.

A Time Capsule is what is known as a "network" drive. It is a network router itself, or it connects to another device that is acting as a router. Backups occur over the "network", which might be over wireless, or a wired Ethernet connection to the Time Capsule.

A simple USB drive is what is known as a "local" drive. It connects directly to a computer and the backups occur this way.....not over a network.

Backups over a network are slower and more complicated than other types of backups. More chances for things to go wrong.

The "local" type of backup is simpler, faster, and more reliable than a "network" type of backup. A support person that knows what they are talking about already knows this.

The Time Capsule might work OK if you decide to connect it to your network router. You can ignore the wireless that the Time Capsule provides, or maybe use it as a "guest" network, so you don't have to give out the password for your private network to visitors. Or, you can turn off the WiFi on the Time Capsule if you don't want another Wifi network.