This is a somewhat common problem for people who have transferred their profiles to a newer console, and with the upcoming holiday season, there will likely be a bunch of people upgrading to an OLED or simply getting a new console. It looks easy to transfer everything at first, but when you start to play, you'll notice that the DLC for Breath of the Wild did not transfer over and and your Master Mode saves are gone.
Nintendo offers the option to open the eshop directly from the in-game start menu, which sounds like a no-brainer. Only that you'll then find out that the DLC will be greyed out, with a notice saying "already purchased", and there is no download button. Even if you manually open the eshop and look for the DLC via the serach bar, will you only get results that are greyed out.
The thing is, that won't ever work. I have no idea why Nintendo even offers the option to redirect the player to a section that doesn't work at all, or why they never bothered to fix it when the "fix" is simple and easy but not well-known.
What you have to do instead, is opening your eshop profile (user icon in upper right corner) and go to a section called "redownload", and then scroll down until you find the DLC in that list. This is, for some weird reason, the only way that actually works.
The good thing is that you will get all DLC content unlocked again with this method, including your Master Mode save files that were seemingly gone. You'll also be able to use "missing" runes again, like the MCZ, without needing to complete the Champions' Ballad again.
