Upload Failed! (401) after "Validating World!" when attempting to upload to Realms

Steps to reproduce the issue:

Step 1: Get your world file (preferably an older world file with any kind of data on it at this point).

Step 2: Click Minecraft Realms on the Title Screen

Step 3: Click on your Minecraft Realm and hit Configure on the bottom middle of the screen

Step 4: Hit Reset World and Upload Existing World

Step 5: Click on your desired world file from Step 1 and attempt to upload it!

Step 6: After 100% (and seeing that your network usage upload drops to 0% in task manager), world validation begins.

Expected Result:

The world file uploads and you can play it on your Minecraft Realm server

Actual Result:

-Upload Failed! (401) on 1.21.5 AND 25w19a (only 1.21.6 snapshot I tested it on and the only one that seems to not be fixed)

-Upload Failed! (500) on 1.21.5 (seems to be fixed on 25w19a?)

Troubleshooting steps I’ve tried:

• Made sure I was on 1.21.5 and the latest Windows 11.

• Trimmed the world file to make sure it's well below 5GB.

• Tried again many hours later.

• Removed all datapacks.

• Made sure I was NOT downloading anything whatsoever in the background that can interrupt the download.

• Trying a copy (some older games had issues or had them fixed just by using a copy of the save file in question).

• Moving the world file somewhere else on the drive.

• Uploading to a different world slot.

• Restarting my computer.

• Using the vanilla launcher with ZERO mods and repeating the above troubleshooting steps.

• Tried another world file on another slot that was significantly smaller to see if I can upload that. (This caused Upload Failed! (500) to occur instead)

• Tried a clean world file out of complete desperation to see if I can get literally anything going. (Only spawn region was loaded and the world size was ~220MB, also Upload Failed! (500) instead)

• Tried ANOTHER test world, also got Upload Failed! (500).

• Restarting my router.

• Trying a VPN.

• Flushing my DNS and IP through Terminal

• Tried using snapshot 25w19a, Upload Failed! (500) did not occur on the empty test worlds but Upload Failed! (401) still persisted on the world file I wanted to upload.

Other notes:

• My world file is around 4.7 GB, but attempts to trim this further below have been futile, it seems to go nowhere.

• Older copies of my world file (THAT HAVE SUCCESSFULLY WORKED BEFORE 1.21.5) give the same Upload Failed! (401), those are also copies that were around 2 or so GB and fewer or no datapacks).

• The world file is still very functional in singleplayer with no issues, I can even host a LAN on it too.

• I am willing to attach my world file if requested, even if it is 4.7 or so GB.

• I am aware this could possibly be a duplicate of REALMS-12980 and REALMS-12617 but I am getting different error codes as opposed to what is being demonstrated and no raw HTML.

• This is an ongoing issue now for me since April 26th.

• Contacting Mojang support regarding the issue via a ticket did not net a fix for Java edition. In fact this bug report was filed after the conclusion of my month long ticket.