[hiidrew]

Would try to target communities that align with your target audience - Twitter, Subreddits, Facebook groups, or Discord. Can also promote more generally on some of these platforms or ProductHunt

Another method, guerilla testing, worked well in grad school. Go to a public place - a library, coffee shop, etc. Politely ask random people to test your project. The obvious downside is they may not fit your target audience, but it's a cheap and scrappy way to get some feedback.