Retroshare is a classical p2p filesharing program, it runs decentralized without servers and is also a great instant messaging alternative and of course you can send files to each other as well, it also has some kind of forum system, friends list and is overal similar to social media. The only problem is getting your ignorant normie friends to use it. At one time in the past I managed to do that and someone even commented "Wow this is better than Fa ceb ook", well I cannot confirm that because I did not use that dubious platform, but I just wanted to give it as an example that retroshare can be a decent alternative to all those things, the only downside is, you need to have friends and get them to use it. I miss the filesharing times, it was kind of hte golden age of the internet and Retroshare is supposed to bring that back I think, but it does not really work that well, because you need to manually find people who use it and connect with them, that is kind of the downside which probably prevents it from growing, but it also prevents it from being shut down, like the older filesharing platforms, so you cannot have everything it seems.
An additional note, it does not run completely without servers, by default the program uses external websites to find out the users IP adresses, so people can connect to each other, so in order to go full dark net mode, you have to disable that and probably look for a tutorial how to set it up, ideally you have friends that are always online probably.