Those changes will ensure that the titles render correctly when formatted using BibTeX. It’s correct BibTeX. The % needs to be escaped, and BibTeX convention is to store titles in upper aw and protect already-uppercase characters with {}.

but for the 2nd part -- some bib(la)tex processors accept bare percent signs, some interpret it as latex does and discard the input until the next newline, and this:

@incollection{citekey,
title = {95% CI 266 to 617 days},
author = {Bentele, G{\"u}nter}
}

does not render on Overleaf for me. \% will work everywhere.

Escaping the %? It's mandatory. % means "act as if the rest of the line does not exist" (used for comments in the doc usually), and because the closing brace of the title is dropped by that behavior, the entry is invalid.

But to get back to your initial question -- what problem are you experiencing?

The first is because you have your titles in title case, see https://retorque.re/zotero-better-bibtex/support/faq/#but-why-so-many-double-braces

The second is just how you enter a lesser-than sign in latex. A bare lesser-than means an inverted question mark or exclamation mark in latex (I always forget which of the two).

The last one is because you have "plain text commands" export on in Better BibTeX. If you turn that off, that problem will just go away.

Except the last choice that better bibtex makes, all the points you've brought are standard bibtex formatting. I think you expect to find things in the bibtex format (not just better bibtex, but the format itself) that are just against how the format works, and I highly doubt that tiddlywiki has a passable bibtex parser. So these are errors in the tiddlywiki bibtex parser you use, not errors in better bibtex.

You might be better off using a CSV export from zotero. Those are easier to parse.