LINKUP - Ultra PCIe 4.0 X16 Riser Cable [RTX3090 RX6900XT x570 B550 Z690 Tested] Shielded Extreme High-Speed Vertical Mount Gaming PCI Express Gen4┃Reverse GPU Socket {23cm} Designed for ITX

https://www.amazon.com/dp/B092JV2BH5?ref=ppx_yo2ov_dt_b_product_details&th=1

I bought this on the recommendation of u/NavicNick, the head Wizard of r/FormD. Do note, though, that it is slightly different than the one that comes with the T1. The one in the link above only has 1 reverse socket (the reversed socket is used on the side that the GPU connects to, and is mandatory for a good fit). However, the side that plugs into the Mobo is not reversed. This makes the cable stick out a little farther from the pcie slot and takes up a little more space, but it allows for a little slack that gives you some more margin of error to work with. It's not a big deal, and it doesn't get in the way of anything, even with my T1 in 3 slot GPU mode. The original T1 riser has both sockets reversed. It makes for a more streamlined fit, but you'll have to get the length more accurate. Idk what the correct length would be, but you can do some digging on that. In retrospect I would have liked the double reverse socket for the cleaner look, but it's not a big deal.

double reverse socket version:

https://www.amazon.com/dp/B092JS4WGJ?ref=ppx_yo2ov_dt_b_product_details&th=1

Edit for spelling.

I have the 23cm single reverse riser cable and it fits my T1 1.1 perfectly

Go for a single reverse. The 18cm double reverse would be way too tight with the backplate, and the 19cm double reverse would have to make some very uncomfortable and tight bends.