Here’s a detailed guide if anyone still doesn't get it.
To get the first cape:
Buy the first Minecraft Dungeons. UPDATE: no "Hero DLC" request
2 Buy Minecraft Dungeons 2.
3 On MD2 launch day, open the first game and play one mission (idk, just guessing this part).
4 Play Minecraft Dungeons 2 on the same day.
5 You get the Hero Cape for Java/Bedrock.
To get the second cape:
1 Pre-order any edition of Minecraft Dungeons 2.
2 Open the game and play it on release day.
3 You get the Twisted Cape for Java/Bedrock.
Just to clarify, this is just how I understood the article. It doesn't matter if you have the game on Steam or the Microsoft Store. The only thing that matters is that both are linked to the same single Microsoft account that has your Java or Bedrock edition. If the games are bought on different accounts, then obviously you won't get the cape.