Would like to set up my a1355 Time Capsule as a general back up drive
This can be accomplished easily if the Time Capsule is connected to the "main" WiFi router using a permanent wired Ethernet cable connection.
bypass the Time Machine function altogether.
Time Machine is software on a Mac computer that has been designed to back up the data on the Mac to another hard drive.....like a Time Capsule. So, bypassing Time Machine.....not using the option.... will be a function of the Macs on the network, not something that the Time Capsule would handle.
I was hoping to connect my TC directly to my iMac with and ethernet connection on both ends.
Understood, but the TC has not been designed to work this way....and will not work this way.
Plan B is to go with ethernet on the TC to USB3 on the computer, a late 2015 build iMac
Understood, but the TC has not been designed to work this way....and will not work this way.
My suggestion would be to set the 10+ year old Time Capsule aside......since it is frankly well overdue to fail.......and instead connect a USB hard drive directly to your Mac.......which will work the way that you were hoping to have the Time Capsule work.
While the TC can be made to work as a hard drive........if it is connected directly to your WiFi router.......I don't think you would want to store any data on the TC hard drive that you cannot afford to lose.
