I can see that you've joined the server. It's not voice only, there are text channels as well. Someone else joined today and has been chatting in the #general channel.
If I recall, the pop up saying your mic is muted only appears at the bottom left of the corner, if you're currently connected to a voice channel in the server. The channels with a speaker icon before them are voice channels. The channels with a pound symbol ( # ) before them are text channels.
If you attach a picture of what your Discord currently looks like when you have the X-S server selected, I might be able to spot what's going on.