Minecraft world has lost everything in latest Bedrock edition

Sadly this is probably due to corruption of your save. Unless you have a backup, there probably isn't much you can do. If the file was on a Realm, realms have versioned backups you could try restoring.

There are a few reasons why this could be:

1. Corrupted Save

• Whilst saving your world, there might've been a problem that caused corrupting what was inside that world.
• You can read @peabody's answer if you want more info.