I've had the same thoughts. I'm new to this like a lot of others so there is a learning curve but I have the same fears you do, that I will miss much of what is out there because I don't know what is available. For example, do I have to be subscribed to the Technology community on every instance?
My biggest fear for Lemmy is that it is going to end up being walled-off silos. I think we are already seeing that in motion with Beehaw defederating lemmy.world and sh.itjust.works. I won't comment on whether that was the right move or not (leave that to wiser people than I) but ff that happens across the platform it could become horribly fractured.
Not sure what the future will bring but I am hopeful that new features will evolve as more people get involved.
I just click the X and it goes away.