AFAIK, these days the content shown when visiting the home page at https://reddit.com is exclusively comprised of subreddits that you're subscribed to. You can visit https://reddit.com/r/popular to see an algorithmic page from subreddits that have opted-in to it, which is mostly dominated by like 50 mega-subreddits but the algorithm is still capable of surfacing small subreddits once in a while (it's not just based on absolute number of votes, it's also has a votes-per-number-of-views component or something). And if you're not logged in, you just get /r/popular when visiting https://reddit.com . (However, I rarely use either of those features, I only have the one subreddit I care about, so I could be inaccurate.)