Uncapped wires in light switch box
If you find out that the yellow cable is hot and switched only by a breaker, you can feed the light from it. Just disconnect the existing light and switch wire from the hot and neutral at the light fixture box. Cap them and tuck them away. Remove any black tape from the switch white wire and connect it to the white wire from the light fixture. Connect the black switch wire to the black light fixture wire. At the switch location, connect the feed neutral to the white wire from the light fixture box and remove any black tape, connect the feed black to the line side on the switch and the remaining black to the load side. With this setup, you can install your smart switch. Connect all grounds.

You have to verify the yellow cable source and voltage before doing any of this.