I fully agree don't do NaNo. Putting aside the organization repeatedly shitting the bed over the past 2-3 years, NaNo really doesn't teach you anything useful other than consistency, and even then it 'teaches' that in the way most likely to lead to burnout. The one time I did NaNo seriously, I got a 35k word project that I feel ill if I even think about touching again.
BUT.
Respectfully disagree with the rest of this post. The more I learn about writing, the more I've wanted to write my dream story. I've solo written 18 novels, co authored another 13, and published most of those. I love working on chonky projects not because of some industrial thing about storefronts and whatnot, but because that's what I have fun with. I like long winding stories, I like being able to write action beats that are thirty thousand words, I like being able to pause and spend an entire chapter just worldbuilding.
My biggest piece of advice would be practice to write what you want to write.
If you want to write short stories, you should do that! And enjoy doing that! Have fun!
But there's noting wrong with writing a novel, and short stories are just as much an industry as novels. More importantly, short stories and novels are different skillsets. If you want to write novels, work on writing novels. If you want to write short stories, write short stories. While some skills cross apply, overall they are different mediums to tell a story, so practice what you want to get better at.
And don't let anyone judge you or try to make you feel bad for writing the way you love. The short one-liner, the flash fiction, the poem, the short story, the novella, the play, the novel, litfic or romance or speculative fiction or fanfiction - they're all different skills and different mediums and all equally valid ways to write. Enjoy writing them the way that makes you happy, practice whatever it is you want to get better at, and if you're looking to make this your primary income - find the area where what you like intersects with what people will read and go from there.
Also, read whatever you enjoy reading the most as well. Just do what makes you happy.