I resonate with the OP because I am in this exact situation that I am building something but I cannot leave my current job now.
When some friends started to build companies in mid-2000/mid-2010 you could code/build something, try to get some traction and you could be received by VCs/angels and occasionally they could write a 25K check for you to work for 3-6 months to build it and perhaps you could get some traction and then scale or go burst.
Now the bar for new products it's absurdly high if you're out of the YC or San Francisco VC circles or if you do not have anyone in the industry; plus most of the VCs prefer to invest in "pedigree founders" than in unknown people, especially if those people are outside of the bay area.
In my first endeavor, I went with a finished product that undercut some big enterprise SaaS vendors, and we lost space for a bunch of non-technical guys with PPTs and one idea.