Facebook groups worked very well for us. If you have social media skills, you could start playing around with content on there as well (depending on your niche).
Online communities like FB, Reddit, Slack, etc are great places to start though.
If your truly beta testing and past the family/friends stage, reach out to potential users. It's good marketing practice too (how to communicate/articulate your value). Assuming the product solves a problem, which it should 🤨... this should be relatively easy to figure out. You just gotta put on those selling pants!
@alex_papageorge1 Thanks for the tip. Do you think personally write to potential users is good approach? Or is it better to leave info about project where they can be and wait for them to reach me instead?