Can you elaborate what you mean? The new forum uses Google Analytics, as did the old forum and does dokuwiki.org. What appears to be new is the use of the Google Tag Manager. If there is any spying going on (that is worse than the usual accepted "spying" like with GA), I'm sure @andi would be happy to change that.
stephane-ascoet trendy(meaning unreadable with awful fonts on a fully eyes-breaking white background almost without drawn structure) layout
A lot of that depends on your personal preferences. And as @michaelsy pointed out, is probably easy to get used to over time.
I understand that the white background can be a problem not to do with preference but with legibility. But there are tools (like browser extensions) that can help with that and are useful to have because the majority of the web is black on white.
I personally find the font very readable. Just looking at the code I found that Flarum uses the system font. That's an interesting decision and I really like it. It makes it easy for you to change, just change your system font (which you should be doing anyway if you find it "awful"). There is a small chance that your browser doesn't support that setting (if you're using IE), in which case you could still change the font through other means.
If you don't like the new forum, that's perfectly fine. But I don't think most of the reasons you gave for not liking it are valid.
I personally don't like everything about it either. But I'm mostly positively surprised by it. I especially like how most of the former forum's content and features have transitioned well.