Unable to connect my time capsule via Time Machine

If you do not want to connect the Time Capsule to the modem or main router using Ethernet and you want to back up directly from your Mac to the Time Capsule.....you are going to have to turn off the WiFi on the Mac whenever you want to back up, run the back up, then turn the WiFi back on at the Mac to connect back to your main network.

It sounds like you are thinking that the Time Capsule behaves like an "external" USB drive that connects directly to your Mac.

The Time Capsule is a "network" drive. It is designed to connect directly to your modem or router.

If you connect the Time Capsule to your modem or router, then you will be able to back up over the WiFi to the Time Capsule.....or.....connect an Ethernet cable from your Mac to the Time Capsule and back up that way.

Please refer to Apple's Setup Guide for the Time Capsule to see how that it is designed to connect to your network. If you do not have the guide handy, we will provide a link. We'll need to know what model of Time Capsule that you have to provide the correct guide.

Let's first make sure that you have the Time Capsule installed correctly on your network.

The Time Capsule has been designed to connect to your modem or your main router.

Then, your Mac will be able to back up to the Time Capsule over WiFi or via an Ethernet cable that is connected from your Mac to the Time Capsule.

From the information in your post, it sounds like you have the Mac connected to the Time Capsule using an Ethernet cable......but we do not know whether the Time Capsule is connected correctly to your modem or main router via Ethernet.

Please provide more details on your current setup. In other words, what connects to what?

for the time capsule to work as intended it should operate as the primary router

The Time Capsule does not have to be the primary router......but it does need to connect to the modem or modem/router in a normal installation.

For it to work as a standalone external, I need to turn off wifi and manually back up?

That is correct, assuming that you have the Time Capsule set up correctly.

For example, here is an illustration from the Time Capsule Setup Guide for a 4th Gen Time Capsule

Here is the link to the guide......if this happens to be the version of Time Capsule that you have.

https://manuals.info.apple.com/MANUALS/1000/MA1575/en_US/time_capsule_4th_gen_se tup.pdf

So, the only way to use this brick is by plugging in to my router?

Apple designed the product to connect to your modem or router, just as the Setup Guide illustrates. There might be someway to use the Time Capsule the way that you ask, but it would be a puzzle for a networking genius. I have not tested the suggestions in the thread linked below, but you could give it a try if you have the time and are willing to experiment.

Using Time Capsule hardwired to Mac for back-up only.

Unfortunately, the information is 4+ years old, so I cannot say whether a Mac running a current operating system will work correctly. LaPastenague is one of the real experts here on the forum, so if he says it will work, I'm sure it did at the time. Hopefully, he will see this post and comment.

I thought I had it correctly backing up before via Ethernet and could see the daily backups, but then they stopped.

As I mentioned before, you can back up to the Time Capsule if you turn off the WiFi on your Mac and use an Ethernet cable to connect to the Time Capsule.....assuming that the Time Capsule is set up correctly and operating correctly. Do you want to try to troubleshoot your setup?

My router is across the flat and at a rather crowded socket set.

You can run an Ethernet cable 300+ feet, or about 100 meters, with no signal loss so you should be able to locate the Time Capsule just about anywhere that you want.

If you cannot run the Ethernet cable, it is usually possible to use a pair of Ethernet over Powerline adapters to send an Ethernet signal over the existing AC powerlines in your home.