I'm facing the same problem on Debian 10 Buster with lyx 2.3.2 and
french accented characters :
- if the file path contains french accented characters, export to PDF
(pdflatex) fails with :
**********
Error message ------------------------ Package inputenc Error: Invalid
UTF-8 byte sequence Latex Error: MIssing \begin{document}. Package
inputenc Error: Invalid UTF-8 byte sequence.
Description --------------------
The document does not appear to be in UTF-8 encoding.
Try adding \UseRawInputEncoding as the first line of the file
or specify an encoding such as \usepackage [latin1]{inputenc}
in the document preamble.
Alternatively, save the file in UTF-8 using your editor or another tool
**********
The 3 above proposed solutions don't work.
The problem does not appear with every document classes, only with some
of them like all koma-script classes, while there's no problem with all
Standard classes.
I'm not sure this bug stays in lyx package, maybe in some texlive
package like texlive-binaries, but I don't know enough about LaTeX to be
sure...
Thanks for caring about that bug.
