I saw a post on Reddit pertaining to the 3000 series cards saying not to daisy chain your power cables. Obviously based on the title I don't have a 3000 card. I have a 2070 Super, and for about a year and a half I have used a single power cable on it. Is that ok? I don't have any problems with stability at all or running games, but I don't want to start a fire or something. I don't have another power cable right now. My PSU is a Corsair RM (2019) 650 W 80+ Gold Certified, if it helps.

 
Single line is always the most practical. Veering off the cable to handle one more piece of hardware is ok though. Try not to hook up more than two on that line.

TDP of that card is ~200 W.
8-pin PCIe VGA power cables are rated for 288 W spread between all connections. I think each individual connection is good for up to 150W.
As long as you're using the cables that came with your GPU or from another reputable source, you should be totally fine.
For that card, I'd only worry if there was some risk that the cables weren't up to spec, or if I was overclocking with exotic cooling.
https://www.gpuminingreso..s.com/p/psu-cables.html

I've always read that while using a single cable might be ok, it's best to use two different ones.