I would not rule out a pinched PEX line. We had one on our 2014 KZ TT. Dealer cut the PEX at the kink and installed a brass PEX coupling. The kink was easy to spot but I supposed one could be hidden anywhere.
Maybe try and follow the braided hose to where it connects to PEX. The braided hose could be kinked too as it is easily collapsed/pinched.
You might try unscrewing the swivel connector at the back of the toilet and seeing if the flow is okay. Could temporarily attach a faucet, extend a length of hose or PEX with a fitting on the end, or possibly let the water flow into a container.