Do you feel like fandom today is no fun? Too isolated, not enough community, too many people policing what you can or can't create? Then do I have a suggestion for you!
DO SOME EXCHANGES!
I'm talking specifically about multi-fandom exchanges, here. Single-fandom or single-ship exchanges can be fun, but they normally happen once or twice a year (unless you do a lot of different ones for different fandoms/ships...) Multi-fandom exchange communities are so active these days that any day of the week you can find an exchange to join in. Flash exchanges, themed exchanges, big annual events, exchanges with small minimums (300 words or even less) or large minimums (10k or more), exchanges where you create in different mediums (art, podfic, crafts).
Problems that multifandom exchanges can help with:
"I feel like I'm posting into a void, no one comments or pays attention to my fic." In exchanges, you are creating a work for someone! That someone, at minimum, should read your work and comment on it. Many exchanges have a specific rule that they have to comment, but even if there isn't a rule, it's strongly expected that they'll comment. (Of course it can happen that they don't, but the norm is heavily in favour of commenting.) Moreover, participants in exchanges will often look through other works in that event, recommend works to check out, etc. Especially if it's a collection of works that revolve around a specific theme, they might read fandom-blind or things that they wouldn't normally check out.
"I can't find other people who share my interests - I like rare pairs, small fandoms, or other non-mainstream interests." Guess what, there are exchanges and events for all of those things! And doing exchanges is a great way to lure people into your specific small fandom or rare pair! Matching with someone who wants a fic for your favourite minor character or niche trope is an amazing feeling, and can be the first step towards making a new friend. And it's also a way for you to learn about other fandoms, maybe pick up some new interests!
"I feel insecure about my writing skills." See point 1 above - you're making a gift for someone! Just as the expectation when someone gifts you a handmade gift is to thank them sincerely for their effort, the norm when someone writes a fic for you is enthusiastic thanks because they made you a gift. People are often just thrilled to have another fic for their favourite ship/fandom/character, let alone one that was made with their specific likes in mind. If you read through the collection for events, you'll see that there are a wide range of skills, and that's fine!
"I feel nervous about liking something controversial or unpopular or that is considered 'problematic', what if people are mean to me?" This is where I think multifandom exchange space in particular is GREAT. The overall culture is very strongly 'old fandom', your kink is not my kink and that's ok. If someone doesn't like your ship or your prompt, that's their problem, and they are still expected to be polite in communal spaces and follow the rules. You will find exchanges themed around kink, including highly specific/niche kinks. Every single archive warning has an event or several geared just towards creating that content. You will see people asking for exactly what they want and what they don't want, without embarrassment and without experiencing harassment. It's a wonderful environment for unlearning shame, if that's something you deal with.
So, you might say, how do I find out about these events? How do I actually join them?
You can join a discord server. The two I would recommend most highly are Exchanges After Dark, which is an 18+ multifandom exchange server and a hub for many events, and the Yuletide discord, which is not only for Yuletide (a huge annual small fandom exchange) but has channels for a lot of other events as well. (If you see this post after those links have expired, feel free to message me and ask for a link.) These are the main ways I find out about events, but they can be large and busy - mute channels you aren't interested in with impunity. Lurk if you wish, just see how the spaces work, or ask questions (but be prepared to get a dozen different answers).
If you really aren't into discord, you can follow this Dreamwidth community: https://fandomcalendar.dreamwidth.org/ - many events advertise there, so you can keep an eye on it and see what interests you, and follow the links back to their specific communities or spaces for more info.
You can look on AO3 under Browse -> Collections, and then select Multifandom, Open, Gift Exchange from the sidebar filters like this. This is probably the least efficient way, since you'll have to wade through many, many collections, but you might find interesting stuff there that isn't otherwise going to come to your notice.
At this point in my life, I feel like exchanges are my fandom, moreso than any specific show or book or movie. Because no matter what I'm currently interested in, I can explore it through exchanges, and probably find other people who like it too, or get other people interested in it. I can have an active community and a social space that is enjoyable and fun and makes me feel connected to other fans.
I am totally willing to answer questions about how exchanges work if anyone wants to ask them! If you're like... aware of exchanges in general but nervous about participating, I can try to provide guidance or reassurance. I want to encourage people who are feeling isolated in their current fandom experience to consider this option!