The latest Nintendo Switch update version has been temporarily suspended as of June 8, 2021. Version 12.0.3 arrived on June 7, 2021, with patch notes stating that this latest update would improve the general stability of the console. The Japanese Nintendo Twitter account made an official statement and revealed more information regarding the situation. Editor’s Note: The update is live again. [Thanks, ryokutya2089!]
However, while an official statement has been made there is currently no solution to the issue. As it stands, a full statement on the situation has yet to be released. With that said, the Japanese Nintendo Twitter account mentioned that if the Nintendo Switch Version 12.0.3 update installs while you attempt to use a microSDXC card for the first time, the card will not work. There is currently no word as to why this is happening.
Additionally, the official English page for Nintendo customer support confirms that this latest Nintendo Switch version update has been suspended. However, as mentioned previously, there is currently no reason as to why. The page does mention that once the software is available for a safe download, it will update.