If you are really not interested, you can read the Six Ancestors Tanjing directly. The text of the altar sutra is relatively simple and not difficult to understand, and there are many famous sayings and epigrams, so it won't be too hard to learn. There are many proofreading books of Tanjing in the market, which can be used for reference, but don't take the proofreading as the standard. Experiencing the original text personally is the most valuable. In addition, the Tanjing itself is divided into Zongbao Edition, Caoxi Edition and Dunhuang Edition. When reading the Tanjing circulating in the market, we should also compare the writing of the earliest new Dunhuang edition (Burton edition). In order to have a comprehensive understanding.
You can also look at the Diamond Sutra. The Diamond Sutra has been a Buddhist sutra of Zen since the Tang Dynasty. Very good. There are many annotated versions of the Diamond Sutra, and the Sixth Ancestor himself has a formula of the Diamond Sutra. If you want to be easy to understand, you can look at nan huaijin's "What Does the Diamond Sutra Say"; For academic rigor, please refer to Professor Gao Yang's New Annotations on the Diamond Sutra. Both books are available in bookstores.
If you are interested in the history of Zen thought and want to know how the Zen thought of "pointing to people's hearts" came into being, developed and evolved, and how it is related to other ideological systems, you can look at Professor Yang's History of Zen in Tang and Five Dynasties and History of Zen in Song and Yuan Dynasties. You can also watch Zutang Collection. Bookstores have them all.
If you want to see the collision between Zen thought and other thoughts, you can look at Notes of Tibetan Monks or Dr. Nabo's Philosophy of Tibetan Buddhism. The former can be found in the library, and the latter is now available in big bookstores.