That’s not a guideline (infinite), its a guide point with a tail, you can’t snap to tails.
Get the tape measure tool and use the red/ blue axis to start the guides, then you should get infinite guides not guide points. You can use the intersection of these.
I tried to draw infinity lines but I wasn’t sure why I wasn’t able to.
I think it needs an edge, red/blue axis seems to work like that, so … thank you very much ;).