I know of a company and their business is basically: identify software products that have customers but aren’t really being developed any more. Buy them and reimplement the software in a more modern way. Sell it again to the existing users, who are generally happy to buy because now they’re getting updates and support and don’t need to keep that old Windows 98 box around because it’s the only thing that ran the old version.
I'll just survey the landscape, and then say it ultimately comes down to personal preference.
So the basic idea is to get an audience and then monetize it. For that, there are different ways. In my opinion it's easier to buy something that gets traffic through this and then monetize it, then to buy a whole business, at least for the purposes of this conversation. Why? Because it's much easier to verify something is getting the traffic a platform's stats confirm, and then build a business on top of that, then to extrapolate correctly from a business someone is selling with a thousand moving parts.
With that being said: plenty of people buy complicated Internet businesses and achieve great results with them.
Also to reiterate from my earlier comment: if you can buy an account (some platforms do allow this) and start with traffic that's already earning a trickle of dollars, psychologically I believe that's 100 times easier than starting from nothing and painfully waiting months to earn a dollar. I recommend it whenever possible.
So without further ado here's how I rank the ways to get traffic. Notice how fractured this landscape this is; most people specialize in one, or perhaps two.
Google SEO: avoid avoid avoid. Not only is it saturated but the search arm of Google is a hard taskmaster. The most frustrating and abstruse of all the ways to make money online imo. I would only do this if I started by buying a niche content website business (aka one with prebuilt traffic).
YouTube: much more appealing than Google SEO but still a grind. However what you will learn here is all useful and the YouTube algo is, in a sense, a great marketing teacher. Unfortunately it takes so long to get off the ground that I'd also only enter this by buying a channel with traffic.
FaceBook: said to be lucrative but I don't know it. This is a great example of what I was saying about secret knowledge. How many people do you know who are enthused about creating FaceBook groups and attracting traffic to them? Yet this is, based on the available evidence, a solid business, maybe even the best of the ones listed here.
Instagram: seems tougher than YouTube in my opinion.
Pinterest: the new hotness, and currently being overrun by AI content lol. But AI + mass producing content is a viable strategy, and your North Star as someone looking to make money online is viable straegies.
TikTok: for profit, most likely better than Insta, and even YouTube. I just don't know enough about specific strategies for it unfortunately.
Newsletters: a good niche but kind of opaque (not easy to learn about and getting crowded). But said to be good.