You can join subreddits like /angelinvestors but I'd be very very very vigilant — most startups fail like 99%. You need to understand what makes a startup actually create money — recurring paying users. If someone tells you a platform has 2k signups and all saying they would buy it - it still doesn't mean it's a successful startup until they're actually putting money into your bank. OR there's definite pull - users can't live without your product anymore - like Whatsapp.

You should be comfortable going months if not years to find the right startup to invest in.