The honest answer is it's almost never one thing the start ups you see featured on those accounts usually did three or four of these in parallel;
Launched somewhere with a built-in audience (Product Hunt, Hacker News, niche subreddits) so they had a "day one traffic spike" narrative even if it was modest.
Had the founder actively commenting in communities where their target customer already hangs out, for weeks before launch. That builds name recognition so when they do launch, their posts land in warm territory, not cold.
Wrote at least one piece of content (blog post, thread, video) that got shared organically. Usually because it had a specific insight or frame that wasn't in the generic AI generated marketing slop.
Had at least one tangible proof point (launch numbers, revenue, case study) that the aggregator accounts could quote.
The accounts that feature early stage start ups are mostly looking for story shaped content. "Solo dev launched X and hit Y in Z days" is a story. A generic "we're a SaaS platform for Z" pitch isn't. The start ups that get featured early have usually figured out how to tell the story before they reach out.