I don't have the time to wade through that whole thing, but I will point out 4 things --

(1) It is NOT a scientific paper, since there is no real science being conducted there.

(2) The reason I can say that is the introductory parpagraph. Notice that, except for the first sentence, every other sentence of that paragraph is a statement that is supported by a footnote at the bottom. This is what is supposed to be done in these types of papers. When a statement claiming to be a fact is made, a footnote is used to explain what research backs up that statement as a fact.

But the first sentence/statement of the paragraph does NOT have any footnotes to back up their claim as a fact. What is that statement?

The rapid and global spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease-2019 (COVID-19) ...

Where is their citation of a paper to PROVE that SARS-CoV-2 is the CAUSATIVE agent of Covid?

There isn't any.

There isn't any in ANY paper ANYWHERE.

The proof DOES NOT EXIST.

That makes the rest of the paper completely moot.

(3) Note the funding. It is all Chinese. That also makes it suspect, even if the paper somehow otherwise seemed valid.

(4) Under Materials and Methods, notice that they were NOT working with any REAL "virus" --

The codon-optimized gene encoding the spike (S) protein from SARS-CoV-2 ... was synthesized ...

i.e. "It was man-made, not natural."

The coding sequence ... was obtained by PCR ... Primers used for PCR are listed in Supplementary Materials.

i.e. "We used PCR to make copies, and then took bits and pieces of that and pretended it was the correct genetic code."

Theses [sic] recombinant adenoviruses ....

"Recombinant" = They did not exist in the real world until we messed around with them and invented them in our computer simulation.