Work for free then equity and pay? (I will not promote)

Ok, so I live in Europe. I have a full time dev job and a family. Mostly Python, some Typescript, GCP, Docker. Web apps and scripting, nothing large scale. I’ve built a few side projects in the last few years but want more. So I was wondering if fledgling startups would be open to an arrangement where I work for free (and part time) in the beginning as an early employee/cofounder but get a small equity and salary IF things go well (like X funding, Y MRR achieved) and increase my commitment over time?