Unfortunately, no.
I would have a single local html page where is possible to render "mathematical symbols". I have tried to download built version of KaTeX, included katex.min.js e katex.min.css as head link and script, but without fonts KaTeX doesn't work correctly. My question is is there a way to insert KaTeX fonts in html just like min.js and min.css? So that I can use html page "offline".

I think you could inline the font files in base64 into the CSS, as hinted at e.g. here.

I have also tried, but I think that fonts are injected "at run time" from fonts directory, so it is pointless insert them in base 64...

katex.min.css has content like @font-face{font-family:KaTeX_AMS;font-style:normal;font-weight:400;src:url(fonts/KaTeX_AMS-Regular.woff2) format("woff2")}. Instead of url(fonts/KaTeX_AMS-Regular.woff2) you should be able to replace that with a base-64 encoded version of that file. (You can probably get away with just one extension version of each font.)

Thanks, I will try!
Maybe in future release we could add this special css