I was a pro game developer for 19 years, more or less. After my last job ended, I self-published an indie game. To this day, it's not made enough money to trigger a single payout. I failed. So it's fair to take my advice with a grain of salt, if not a whole block. But here's my two cents anyway.

Start by sketching and writing. Think of verbs; games are all about doing things, even if it's just advancing through a conversation. Your protagonist is a cat, so cats run, jump, explore, play. Think of why the protagonist is doing things. Where do the missions come from? And in this case it's hard not to look at Stray. There's almost always something that's come before, even if it's not super high-profile like Stray. Think about what you want to do different.

Art will come from you, if you go it alone and can't or don't want to buy art assets. Blender and GIMP are hard to learn, but free and powerful.

Your engine is almost certainly going to be Unreal, Unity, or Godot. Each has strengths and weaknesses, including the cost of use. You have to factor it all in.

I do think you're right that you'll learn more by making things than doing tutorials, but be aware if you start spinning your wheels on something. You'll benefit from both.