Hi, Michael
>   Are you sure this is a new problem?
Yes, previous code snippet using (getenv "PATH") when tramp not involved which is right result, I've tested this by revert this commit.

>   I've tried Emacs 26.1 on MS Windows, and I get a similar error.
Have you added related path to PATH environment variable, e.g. d:\emacs-26.1-x86_64\bin ? I've download Emacs 26.1 from
http://ftp.gnu.org/gnu/emacs/windows/emacs-26/emacs-26.1-x86_64.zip
and it shows fine.

Best regards,