Like any other "language" theory about a manuscript, the Chinese theory has many assumptions and gaps.
First, as far as I know, it is based on statistical similarities and the fact that "word repetition" occurs in many Asian languages. However, in my opinion, this is not enough to directly claim that Voynichese is a Chinese or Vietnamese language.
Secondly, after a long time, we still haven't understood how the proposed transcription system used in the manuscript works. If it were based on Chinese, we would expect to find more parallels, as it's unlikely that the author didn't try to simplify a language that wasn't similar to the European languages they were familiar with (it seems strange that the author's system would be as complex or even more complex than the Chinese language itself. We must remember that this is the Middle Ages, the author is a European, and for him China was more, say, "exotic" than for us now).
Thirdly, why is this book incomprehensible to us? Why did the author, who wanted to write a work in transcribed Chinese that would be understandable to other readers (if you say that it could have been the author's personal reference book, you'll have to explain to me why the author worked so hard on it? Have you ever seen large, detailed maps on nine pages in regular diaries?), not explain how to read it? There is the Codex Cumanicus, where the Tatar language is listed at the beginning and written in a way that European missionaries could read and understand. This is the simplest and most practical approach, which we don't see in the manuscript.
Fourth, the author's motive is unclear. The book does not contain any topic related to China. Judging by the illustrations, the manuscript is mostly a medical reference book about plants, their medicinal properties, and additional information about anatomy (the so-called "balneological" section). However, there is one "but" - the f68r1 and f68r2 diagrams, which may depict the Chinese lunar month (simple and sacred, respectively). However, this coincidence alone is not enough...Why would the author use an obscure transcription system to write a reference book that he (or other people) would have to use constantly?
Fifth, translations... There are meaningful ones, but often the approach to them is subjective, and I haven't seen any general and trustworthy methodology yet (but maybe
I'm the only one who didn't see it).
Sixth, I would like to hear why the system is like a cipher and contains its own internal features. If you try to convey Chinese as accurately as possible, but inconsistently, I don't think you will encounter any "anomalies" or peculiarities in the text.
Seventh, a personal question from me...
Do you remember Gerard Cheshire? For me, he became the embodiment of all linguistic theories. You should explain how you differ from him (Cheshire selected roots from all European languages, deriving a meaningful result from them, but you know how correct his method is. It will be difficult to select from Chinese, of course, but you will have to resort to something similar anyway).
However, it is still possible to come up with some indirect explanations for the peculiarities of the manuscripts. For example, it could have been a group of merchants who regularly visited China and had a basic understanding of the Chinese language (which was sufficient for them to negotiate and establish contact with the Chinese), and who decided to write a book for a limited number of people (perhaps their colleagues who traveled to China, or perhaps someone else). The fact that they did not use Latin can be explained by the fact that the merchants did not find a method of romanization (and simple transcription seemed either redundant or inaccurate to them). If the book was written not by merchants, but by hired scribes, it is possible that the merchants provided the scribes with texts in Chinese and explained how to write them, and the scribes, who did not know Chinese and did not understand what they were copying, translated the text without questioning what they were writing (in fact, this "fluency" of writing is evident in the balneological section, with many repetitions and similar words, and a large number of qo- although they look similar to the Asian language, it feels like they reflect its subtleties very poorly.
In general, one can even say that balneology was not written by a very skilled person. This is consistent with the fact that there is always more text on the pages of the balneological section than on others, not taking into account the recipes that were written by the same person, and it is logical to assume that the scribe would be looking for a way to reduce his work. This statement is suitable for any language as well as for any cipher version. But it doesn't really matter now...).
In conclusion, I believe that although this version is more substantiated than others, it still contains many inaccuracies, liberties, and assumptions.
Remember that you have the power to correct these issues! 
P.S. If anything, sorry for bad English. I I use a translator to communicate here, forgive.
