The first thing that comes to mind in terms of him and high-level inscription patterns is when he walked through the pattern of the Thousand Illusionary Array at the Void Illusionary Divine Palace, something not even Martial Ancestor Realms could do. Now, that's not decoding per se, but then you look a few chapters later when him, Wu Yazi, and Xiao Yu are in the treasure room, and he destroys the Celestial Bound Array, something that could incinerate Dao of Dragon experts. Now, if we consider the fact that this Legend rank inscription probably wouldn't be able to affect someone above the Heavenly Fate realm, then by that logic it would be even more difficult to make either of the two aforementioned arrays because of how much stronger MAR/DODs are, and it's described how he navigated them with ease. Finally, it's described how he knows how to utilize the Myriad Spiritual Sword Array, something that can not only kill Deity ranks, it was able to kill the Sage Emperor's generals, and we can infer that he was self-taught as he didn't need Tian Yuan's help to comprehend it.