João Lemes

Just adding that @frailsnakeq workaround worked here. Archived game, clicked on the game icon on the home menu to redownload it, did the replace world process and this time it sucessfully uploaded it (showing the Error screen at the end). Entered the realm on the W10 version and downloaded the world correctly.

Tested on my Switch and it didn't work. I knew it would still have the Error pop-up, so I entered the realm and it was just an old world that was already saved there, not the one I desire to upload. The upload process remains the same, try to replace world, go to the Initializing Upload screen and shortly after the Error pop-up. I even tried to stay in the pop-up screen for some time after it show up, but nothing different and the world was not uploaded. 

Don't know if this interfere in anything, but my Nintendo Online subscription ended some days ago while I waited for this fix, so I can't enter the realm on the Switch console itself, but it still allows the upload (well, it looks that it allows at least, since I do all the replace world process like normal). So I am using my Windows 10 version to enter the Realm and test it.

I can reset my realm from the Switch now, couldn't do that before the 1.16.2 update, so it's something.

Would add that, like Amanda Haines said, if I go to the console home and try to close the game, it freezes my system and the only way around is to do a hard reset, holding the power button for some time.

I'm having the same issue: can't upload my game using the Nintendo Switch version. I also have the Windows 10 edition and there it works perfectly, but what I wanted was to transfer my world from the Switch to my PC, and the work around can't do this.

I tried many times but not even the seed of the world was uploaded. I request the upload, it goes to the Initializing Upload screen and 1-2 seconds later it show the Error pop-up "An error ocurred". Tried uploading in both the Realm pen screen and my world pen screen, tried entering my world before uploading, tried resetting the Realm (which works in the Switch version) and then uploading, tried another wi-fi connection, tried in different times of the day. All to no avail.