recommendation for external 1TB SSD as a Time Machine Backup

I’d suggest a 4 to 6 terabyte hard disk drive (HDD), as you don’t (usually) need the speed of an SSD, and as you will want storage capacity sufficient to maintain some depth of Time Machine (TM) backups.

I’m working with a mix of NAS storage units (with TM support) and Seagate external HDDs. NAS isn’t cheap, but adds flexibility and hardware data protections, and can consolidate multiple TM backups into fewer boxes, and with fewer or no wires which is particularly handy for portable Macs.

For your iMac usage, a ~USD$120 4-6 TB USB HDD will probably be the best trade-off.

Smaller disks used as Time Machine targets can tend to have issues when they get close to full, too. TM does not “like” big files in small targets, and can have difficulty pruning backups with a relatively too-small target and relatively too-big newly-arriving files.

Buying a SSD for backup is kind of a waste of money. Buy yourself a high quality External Hard Disk such as a OWC Mercury Elite Pro but if you insist then get a https://eshop.macsales.com/shop/owc-envoy-pro-ex-thunderbolt-3

I have used Samsung SSD's and no issue. Presently I'm using a WD NVME drive in a USB gen 2 enclosure. You did not state the size of your internal drive. Your TM should be >2 x the size of your internal file size (not necessarily the drive size) so you can contain some history without filling up. Just a matter of cost vs speed. I have several Mac's so having a TM that is fast is handy when restoring.

Some like them, I do not. Again, there is no benefit to using a SSD however if you want a lower cost solution consider:

https://eshop.macsales.com/shop/firewire/on-the-go and a https://eshop.macsales.com/item/OWC/MOTGPWR/

I like the Sandisk Extreme SSD's

Small, rugged, portable, bus powered and fast. They come with a USB-C to USB-A adapter, so they can directly plug into the USB-C port on the 24.