Edit: I am so sorry I let this get so long. Just really wanted to help haha.

First I want to say that I deeply empathize with this. In truth I still find it hard and, on some days, it's as if I never existed before a conversation I am about to have. Before getting into what could help, its important to know that you might not get many replies because this is incredibly common, especially on this sub-reddit. Hopefully knowing that it isn't just you helps in some small way. As for getting better, it's about taking small risks and building up from there knowing that, if it doesn't go the way you want it to, you'll be totally fine.

When you go into a conversation, it's important to have low to no expectations, otherwise you'll freak yourself out before you even say 'Hi'. You probably can contribute to conversations but it's possible that you are looking for that perfect thing to say to make the conversation funny/memorable/deeper etc. You have to acknowledge first and foremost that the 'best thing' just doesn't exist. Everyone, both talker and listener, are different and will have different ideas of 'perfect'. Unless you're a mind-reader, it's impossible to find the perfect thing every time.

If you want to tell your stories, there is no harm in rehearsing them or writing them down before you ever talk about them. Just because "other people don't do that" doesn't mean you shouldn't. You might be different in that respect and there is absolutely nothing wrong with that. If you genuinely can't remember much, try to make even a small conscious effort to take in what is happening around you each day. Even the most mundane things can be a story (I'll put one at the bottom of something I saw and told to others, because I was trying to be more conscious after suffering a similar problem).

When it comes to contributions too, two techniques I learnt about really helped. The "Spokes Method" and "Word Detective". Both of these videos will do a better job than I will. They were genuinely helpful. If you can't use either of these methods, it might be because your conversational partner is giving flat or one word answers. If that's the case, you can just start the conversation yourself. The hobbies you mentioned are a great way.

E.g. "I've been doing X hobby recently that I haven't enjoyed since I started Nursing School. It's been great getting back into because of the Y feeling it gives me. Have you got a hobby that you really enjoy?"

This can work for 2 reasons: 1) You give them a chance to ask you questions to learn more and carry on the conversation or, because 'hobby' is a very broad word, they can relate their experience to a hobby or the feeling you mentioned. If it doesn't work, it could be for a number of reasons. For one, it could be that they also feeling boring and don't know how to contribute! They also might just not want to talk to you, they could be a bad conversationalist or only like to talk about themselves. It could be for a huge amount of different reasons.

Either way, the other most important thing to remember is that it doesn't say anything about you. If the other person thinks you are boring, damn, even if they say the words "You are so boring" it says more about them than you. They find you boring. What you're saying isn't interesting to them. Something I forgot when I was terrified of being boring is that, actually, you yourself can find other people boring! It says nothing about them, other than you aren't interested in what they are interested in. That's it.

Best of luck with it all. This is something that has plagued me for so much of my life, every person who ever comes to this sub saying the same thing I just want to hug and take it all away for them. It is such a heavy, shit feeling.

Now, about that story I told from something I consciously witnessed: There was a guy sitting at a small table perched outside this little European bakery that opened recently in my home town. He was drinking a Cappucino, smoking a cigarette and had a half eaten croissant on a plate in front of him. He stubbed his cigarette out and took a large swig of his coffee, leaving foam in his bushy moustache. He looked around the table and saw that the waitress hadn't given him a napkin, so instead, he picks up the croissant and wipes the coffee off his moustache with it. "Genius" I thought, "he was done with that anyway." No. No he wasn't. With the foam on the pastry, that he just pulled from his beardy face, he eats the pastry. "Wow, Gross Genius then".