In this excerpt from a Bitwig Studio Grid walkthrough, the presenter demonstrates how a low-pass filter behaves at its core: it slows down a signal, preventing it from jumping immediately to its next value and instead easing it there gradually. That behavior is identical whether the signal is audio or a stream of pitch control data.
Pointing the filter at a pitch signal instead of audio produces portamento. The cutoff frequency becomes the glide rate, and the lower you set it, the slower the pitch transitions. It works, but using a frequency parameter to control timing is an awkward mapping.
A lag module or averager does the same job with more intuitive controls, and right-clicking any module in the Grid surfaces related alternatives. From there, you can go further, running faster glide on high pitches and slower glide on low pitches, since the Grid gives you full control over that behavior.