I have a new router and no longer need that capability from my time capsule. How do I connect and configure the time capsule directly to my imac and use it ONLY as a backup

The best way to do this is to reset the TC to factory and plug it by ethernet to your main router. Use the airport utility to configure the TC in bridge mode and you can turn off the wireless.. so it will become a dumb hard disk on your network. You can then backup to the TC over your normal network.

If you plug the TC directly into the computer it is quite a messy setup.. possible but IMHO not worth the hassle. Happy to show you the how if you really want to try it.. but I will need a stack of info about your setup. (link below to older set of instructions which should still work)

NB.. if you are running Catalina on the iMac please don't bother doing this.. sell off the TC and buy a simple USB disk.. it is faster and more reliable than the TC ever will be. Apple has changed a lot of things and the TC is really no longer suitable.

Here is the link from long long ago (not so much a galaxy far far away) when I was young (ish) and stupid.

https://discussions.apple.com/thread/6486672

How do I connect and configure the time capsule directly to my imac and use it ONLY to backup my iMac on a schedule?

The Time Capsule won't connect directly to your iMac. A USB drive would, but the Time Capsule is not a USB drive. Instead, the Time Capsule will connect to your new router. Then, you can back up to the Time Capsule over the wireless network provided by your new router.

You won't need the wireless provided by the Time Capsule, so that will be turned off and the Time Capsule will act like a wired back up hard drive only.

If you need help with this, we need some basic information......

1) What is the make and model number of the new router?

2) Will you be using a Mac to reconfigure the Time Capsule? If not, a PC? An iPhone / iPad?

Sounds like it's time to retire the time capsule.

If you are running the iMac on Catalina.. YES.. definitely retire the TC.

Using network backups makes loads of sense with laptops. However on a desktop computer plugging a USB drive into back of the machine is easy peasy and much the better method.