IO26 (and IO25) support digital output (setting the pin high to 3.3V or low to 0V), as well as analog and digital input. The additional IO pins exposed on the underside pads also support capacitive touch sensing. Just be mindful that you cannot source or sink much current through these pins. You’ll need a digital switch circuit to service higher currents.
For an example of how to use them as a digital output, check out this code.