I'd simply have been more patient with myself.
It's amazing how little my startup has evolved since I launched in 2016 -- so much time and brainstorming spent trying to "optimize" every little thing, but resulting in very little actual change. The initial ideas was a good one, and it's what my clients like best.
I wish I'd just been more patient, trusted the process, and invested my excess energy into something more creative, or something else entirely.
I would probably take more time learning non tech skills like marketing or design. I enjoy programming and have gotten pretty good at making robust products but always struggle finding ways to get it in front of people.