One consistent over the course of Star Wars is that anytime there is a political discussion or battle planning the movies begin to greatly lull. Politics and Star Wars are a combined snooze fest and so would a series about Mon Mothma because that is what would be the heart and soul of it.
Mon Mothma herself isn’t a very exciting character. She dresses in white and has short-cropped red hair. She also speaks in a smooth monotone, almost ASMR inducing tone that makes one’s eyelids droop, but if Cassian Andor is worthy of a series so would Mon Mothma.
Her show would be set up about the same time period as the Cassian Andor show. She would be a senator in the still established Galactic Senate but would be working to set up this rebel cell behind the scenes.
There would be a lot of intense political drama, and she’d have to do a lot of work to convince others to join her cause. It would be a show that could be done on the cheap as there wouldn’t need to be a lot of space battles or action for that matter. As a political drama it could work, but it would be about as exciting as two scoops of vanilla ice cream.