Think of a season of a comic like you do with a season of a show. I like to think of a season to be the completion of a big story arc that contributes to the main plot. I can't really describe the way I know seasons end, I kind of just do? But I'm gonna try: I think a good way to know when one season ends is if you feel like the story drastically changes at that point, usually this is a major plot being introduced that becomes relevant. However since yours is an episodic format, maybe make it so that each story is an individual season, kinda like Infinity Train?
Also don't feel like you have to limit yourself when it comes to outlining a season. A short, 20-30 episode season is nice, only when your story is compact enough to fit into those amounts of episodes. Plenty of comics have 60-90 episode seasons - hell, the first draft of my comic's first season is 59 episodes (58 if i combined the last two episodes together, since the last one is really short). One of my favorite webtoons, Hooky, was near 160 episodes before it stopped and launched its final season, and it never felt like the story dragged on or anything. The Croaking, a comic nominated for a Ringo Award, just finished its first season with 90 episodes.
What's important is that you're able to properly tell your story and the amount of episodes is irrelevant to that, most of the time, readers aren't gonna care how long it is. Sometimes stories get so big they really can't be told in 30 or so episodes, ya know? Kind of the beauty of publishing comics yourself. You decide how long it is.
Maybe it's different for novels, but I've never seen a comic reader who complains about a season getting too long, haha.