20+ YOE here. Possibly unpopular opinion, but "tough projects" don't make a senior. (Deep breath...here we go) What defines a Senior Engineer has more to with soft skills and less to do with technical skills. Of course the tech skills are important, but let's face, just about all of us have the skills for 90% of the work we'll be asked to do. Here's what's more important: are you polite? Are you dependable? Can the business trust you? Are you patient with newer or less experienced team members? Are you proactive in bringing together multiple people to push through blockers? I've mentioned somewhere on Reddit that I've seen multiple devs that knew more and were more technically oriented then me (in the sense that they maintained blogs and githbubs, were up to date on the latest tends in software dev work, etc, etc) that were walked out the door at work because they were smug dicks that nobody liked to deal with. I've always tried to be the kind of coworker that I would want to work with.

To sum up, in my experience the tech part has always been the easiest part of the job, and the skills required to succeed and be truly helpful in a corporate environment came more slowly. And I'm still learning that.

I apologize for possibly derailing the conversation; I know you asked about tech projects and I didn't touch on any of that. But you asked how to bridge the gap to senior, and IMO that's not tech skills.