Looks very bad. It simply will not eat. Or drink the homemade pedialyte.
It simply shakes its head and sends it everywhere.

Have you tried baby food? Without onions. If it is getting weak, at
this point I would try to feed it just about anything that it would
eat, maybe potted meat or something similar, they tend to love the
smell. I'm sure it's not good for their tummy(so please, nobody fuss
at me), but at the starvation point, I will try anything with a little
one. I think your biggest concern should be getting it to drink. I
found with mine, I had to wrap her in a cloth very tight so that she
couldn't wiggle, and hold them as close to flat on the belly as you
can, if necessary hold it up until you get it to take the formula,
then quickly change it's position. Once you have them wrapped up,
wait for the crying to start, then use the bottle, or whatever to drop
milk in its mouth. Once might tasted it, I had to literally take the
bottle away when she had enough.

You may have to let it play and wear itself out, I have found that
with an older kitten that has been with its mom, it is their instinct
to fight you. Check for dehydration by pinching the skin gently at
the back of its neck and pulling it away from the neck(very gently!),
if it doesn't spring right back withina second or two, the kitty is
dehydrated, forget about formula, and get as much of the pedialyte
into him as you can.

I have also known kittens of this age to greive themselves to death
because of the loss of their mother. You also do not know what it
might have been exposed to, it may have gotten something from the
mother. Sometimes there is simply nothing you can do. Definitely get
it to a vet, but if he doesn't make it, don't blame yourself. It
sound to me like you have done just about everything you can.