The algorithm chicken-and-egg problem is real, but Reddit's spam filters are actually your biggest hint at what works, genuine community participation over months before you ever mention your project. The platforms that seem most restrictive are often the most rewarding once you're established.
I've hit this same wall repeatedly, built product after product without knowing where to even start looking for users. The depression from launching into silence is brutal. I'm currently building something to help with this exact problem and would love to give you free access in exchange for honest feedback if you're interested.