You can't bank on a new project having any significant financial success, or much traction at all really, especially if it's your first rodeo. Making money is mostly about validation, talking to potential customers, and iterating on ideas, not coding. While they are great skills to learn, it's not a particularly efficient way of beefing up an engineering resume.
I do think it's good advice though to build some stuff while interviewing. I'd focus on small projects that can be built and shipped in a month or so, and do a few of these alongside interviews. Also be sure to put effort into nice landing pages--people judge by appearances.
Even if it doesn’t make revenue, it’s still a years worth of xp on a resume.
I think there’s pretty much zero chance of getting a programming job with a four year gap and no meaningful projects. But add in lots of commits showing off good design and coding decisions and it’s easy for a company to understand value and hire.
A few of the popular buzzwords to start a project with: Next.js, Prisma, Supabase