Oh boy, I love talking about my writing process, thanks for asking.
Most my stories (unsurprisingly) stem from my own fantasies, what I find most enjoyable. Usually just scenes will crop into my head, and I'll give it a lot of thought and see if it can expand.
TBH, most can't. The most they can be is short stories, if not just basically one scene.
But some of the ideas I have I find have legs. They get more delicious the more plot I add, as far as I'm concerned. I find the ones that do offer me an idea to explore through the story. Dream Dungeon is honestly about what people may be afraid kink is vs how great it can be when it's done with someone who cares. Too Big To Handle is about what people tell you you should want vs being unafraid enough to go after what it is you actually do want. The Contract is about... I'll let that story grow a little more before I spoiler it
Once I know what it's about, once I know it has legs, an outline kinda just forms in my head? I know the ending of any longer piece I make (except a few of the earlier ones... wonder why I didn't finish them. Though I do know DD's ending, I just had Life come up which kept me from completing it... yet). I know the major "tent poles" if you will, the major moments that drive the story. I don't always know the smaller moments and I feel like I discover a lot along the way. Sometimes I have to change tent pole moments when I've realize my story no longer built to them or my characters no longer did (i.e. Did you know Ari in TBTH was supposed to have a brother that passed away? Of course not, it later proved to not be important to the story).
So I guess I'd say it's a mixture of the two. There is an "outline" in my head, but I allow the story to also grow organically. I have moments in writing where I have to pause and really think, which leads to me deleting things, because I realize while what I'm writing works for the *scene* it doesn't support the overall story I'm trying to tell. My last chapter of The Contract was like that, I wrote it one way... but realized I had written fine good scene but not one that fit my story. So I had to edit a lot of it until it came to a place I felt like was going to actually build to what I want it to be, to where the story needs to get to.
But usually, the organic stuff is what makes writing fun sometimes. In a way, even though I know the ending, I don't always know how we're exactly going to get there. It can be stressful when you wished you set up something earlier or wish you didn't make a promise in chapter 1 that you no longer, like... want to fulfill. But I think TV shows have the same pain, it's just part of writing for something that you have to publish part of before you've actually written the whole thing.
Hope that helps somewhat
Or maybe it was just cathartic for me to write