#5006 did it for the codeblock enviroment.

however, in other places (i.e. in most places), curly quotes are used.

I can only find one such place, added recently:

$ git grep -C1 "tcode{[^}]\*'" *.tex
compatibility.tex-std::format("{:*^{}}", "", '1');    // ill-formed, previously returned an
compatibility.tex:                                    // implementation-defined number of \tcode{'*'} characters
compatibility.tex-\end{codeblock}

At least in Chapter 5 ([lex]), most single quotes (e.g. single quotes in \tcode) are rendered as curly ones.

#5006 did it for the codeblock enviroment.

Thank you for the link to the related PR!

My grep above didn't pick up any other ' in \tcode. But in [lex], I do see curly ' in the grammar.

You can use something like

grep --color=auto -n -P '\\\w+\{[^}]*'"'"'[^}]*\}' *.tex

(This assumes GNU grep and there are some false positives.)