My XFX Radeon RX 5700 XT RAW II seems to work fine running off board power on my 4,1 -> 5,1. I used two mini 6 pin to 8 pin (6+2) cables

Here's a mini 6 pin to 8 pin cable. Then get a mini 6 pin to 6 pin cable.

https://www.amazon.com/Express-Video-Adapter-14-inch-COMeap/dp/B078ZRDLNR/ref=sr_1_11?crid=2A3994BSIFVGU&keywords=mini+6+pin+to+dual+8+pin&qid=1649544584&sprefix=mini+6+pin+to+dual+8+pin%2Caps%2C79&sr=8-11

I'm not an expert, but the internet says that card maxes out at 262 watts, and I think 2 power cables + the PCIe slot can provide 75 watts each, 225 total.

So the card can't use as much power as it wants to which might make the system unstable/kill the psu. You could do a Pixlas mod, but that is outside of my experience. You might also be able to tap into the power cable in the optical drive bay, but I'm not sure.