Ok, thank you, but to be clear, since I wish to "learn" as best as I can to be able to solve future problems in a short amount of time, can you tell me how xaero mods can break the game? I mean, it's probably because of some of the latest mods that interact with it that I added yesterday that may break it, because before there weren't a single problem, letting aside the fact that every time I clicked "Singleplayer" the game crashed, but every other thing was working.
Update: I forgot to note that every time I start the game I get a notification from Minecraft saying "Resource reload failed" and then it crashed, now, after removing all the xaeros mods, I still get the message but the game doesn't crash. I'm now doing the test with Exaroton.
The server keeps crashing, here is the log: https://mclo.gs/HeyLSbJ
Is it possible that a certain "Stairs Block" might not load correctly? Its texture or model, that could be why I get that message, but in Minecraft and mods there are so many different "Stairs block" that finding the specific mod that creates that problem might be impossible but the log is just reporting it, at this point I let you do your job since I don't know what to do anymore, this is my way to help but I might just slow you down.