In academic writing, such as a maths textbook, is the author most likely taking a stand against wokeism if they not only insist to use the generic 'he', but also refer to the reader as 'man' and readers as 'Gentlemen'?

The answer is a solid “maybe.”

Is a maths text really academic writing? Maybe. They are scholarly, in that they are published by scholarly presses and written by experts. However, they are not peer reviewed and, assuming someone is willing to pay the publication costs, could say anything.

It would also depend on when the textbook was written. The textbook would have to be very recent. For much of history, maintaining a generic ‘he' was standard. Also, your example of referring to readers as ‘Gentlemen’ dates the text in question and seems quite bizarre for a textbook. I've read a lot from textbooks, (admittedly not in maths) and breaking the 4th wall to address the reader as anything is very nonstandard.

Finally, you would have to look into the author(s) and publisher. You might be able to make a case for it if a vast majority of them had publicly made any political statements and they blatantly agreed with an “antiwoke" position.

In the end. Probably not.