It may/may not be useful, because mdbook does not provide single file webpage. So, may be there should alternative way to display the manual in AnkiDroid app.

That would require us to treat the manual as a "mini-web-site" instead of a "bundled web page", however the main constraint is still the size of the average mobile screen. Stated differently: whatever way the manual is presented it needs to be responsive design, and gracefully display on tiny screens. If mdbook does that, great. If mdbook does not do that, it is not acceptable

I think mdbook displays nicely on small screen devices.
But going through docs of AsciiDoc, I came knew that sidebar can also be added to AsciiDoc.
So, I will first check if AsciiDoc can be used to make the manual more presentable then there is no need to consider mdbook.

@mikehardy https://docs.ankiweb.net/ seems to work well on my mobile (only complaint is that buttons are a little small), does this seem like a reasonable approach given the link?

Sure, if you have a sidebar and it's take on responsive design is to be collapsible via a hamburger menu, default closed on small screens, that's pretty standard and works well. Any solution that does that looks good

Okay, I will go through this approach.