There is a vast array of alternative economic systems proposed over the last century, and much of it can be labelled socialist—it’s a big ask to expect someone to describe a fully realized alternative in a forum comment, when they can just refer to the body of work on the topic.

I mean, this is ELI5. I also don't think it's reasonable to ask the 5 year old to read all of marx? The task is to teach, even if slowly. Maybe we can talk about specific small examples? Like you mention how capitalism has failed to put the homeless in the houses they sleep next to. How would your favorite flavor of government solve this?

As an example, capitalism tries to manage empty houses by making it inefficient to buy land and have it sit empty: others who use their land while they let it appreciate will get ahead of you, and as you fall behind the market you'll eventually be compelled to sell. (I'm not saying this is a good system, and I don't particularly care about how it's wrong; this example gives a floor for other theories to compare against and shows a bit of the system can be explained in a short forum post.)