How can I scale up my impact on a small team?

Some thoughts from me:

• Thousands of users is where bugs are interesting - Interesting in that the volume should be pretty substantial. A challenge you could take on is figuring out how to make website completely bug free. It's probably not possible, but having this mentality can be a good guiding force to push you to write better code. You could potentially create workstreams around adding test coverage, more alerting, etc.
• Use data to influence the roadmap - A concrete goal you could take on is, "I want to be able to convince the company to execute on a new project due to the data-driven case I've made for it." This happened at Meta all the time, and it's an extremely important skill to have, especially when pushing for more senior levels. This is why it's a great place to be when you are very good with data!
• Expand your team - One of the more straightforward ways to build more scope and senior engineer skills is to have more people. When you look at the technical landscape of your company, can you come up with projects that would be both high-impact to the company and require additional headcount? If you can, you should run that by your manager and see if you can work together to expand the team. It's a win-win for everyone as you get more software engineers to lead and the company has more employees adding more business value. Being able to create scope is a super important skill growing from mid-level to senior.