automatic backup on new iMac 2020

Time Machine will not backup to iCloud.

Also see the following from Back up your Mac with Time Machine - Apple Support

Connect one of the following external storage devices, sold separately. Learn more about backup disks that you can use with Time Machine.

• External drive connected to your Mac, such as a USB or Thunderbolt drive
• Network-attached storage (NAS) device that supports Time Machine over SMB
• Mac shared as a Time Machine backup destination
• AirPort Time Capsule, or external drive connected to an AirPort Time capsule or AirPort Extreme Base Station (802.11ac)

with my iMac (2019) i use a WD "my passport" external HDD connected to one of the usb ports on the back of the mac for time machine duties. but i would like to let you know, i only do a backup about once every 7 days, so not a lot of work for the disk. and i keep very little on my internal drive. also, in using macs for a decade i've never needed to restore from TM. if you are using auto backup and/or using it for work or anything critical, you may want to look at an external SSD. if you do decide to go the SSD route, i recommend shopping at OWC to find the drive. they test what they sell on macs.

WD = western digital it's a brand name

HDD = hard disk drive or hard drive for short

SSD = solid state drive - fairly new technology. it does what the hard drive does with NO moving parts - much quicker than HDD but also more pricey. worth every penny in my opinion.

Personally I use a redundant backup plan.

On External Hard Disk #1 I have Time Machine running.

On External Hard Disk #2 I have SuperDuper do a backup at 2:30AM every day.

Why redundancy? Very simple, backup EHDs can fail too. I've experienced this personally.

With ANY backup system you should check it periodically (1x a week is fine) to verify it is working okay and when it isn't then you can troubleshoot it to get back on-track.