Who ever marked as resolved marked it as duplicate, Meaning theirs already a thread about this. Now if that's not the case then someone decided to mark it as resolved for no reason and they probably weren't a moderator. Let the mods do there job and stop acting like one. Alexi has a reason to be frustrated as Alexi has been trying for months to fix this. The only thing I can tell you is calm down, relax and create a new account to sign in with. If it still happens then I think its something wrong with the game. If this is a duplicate there should be a link to click on to see the other thread that was open before this one.
This is also happening to me, I tried copying the world but that doesn't work, I download a world file from my expired realm but It still wont let me in that and it says the same thing over and over: Unable to connect to the world. Please check your connection to the internet and try again. For some reason the worlds that do this are mostly because they have a lot of command blocks or behavior packs. I have a world that's over 100MB but it doesn't do that so I don't think its the world size that's causing the problem. (I'm on windows 10 1.16.100).
I dont know if this helps but, I uploaded the same world that has this problem to aternos which is a server hoster and the world works just fine, so its not the world, I think its the game. (Im on windows 10 edition 1.16.100)