expl3.sty error

[Rich Shepard]

Good morning, all:

Compiling a document with pdflatex throws this error:
LaTeX Error: Mispatched LaTeX support files detected.
\ExplLoaderFileDate{expl3.sty}

Looking for expl3.sty I find:
/usr/local/texlive/2023/texmf-dist/tex/latex/biblatex/blx-case-expl3.sty
/usr/local/texlive/2023/texmf-dist/tex/latex/l3kernel/expl3.sty
/usr/local/texlive/2023/texmf-dist/tex/platex/base/plexpl3.sty

Checking the dates on each shows:
Dec 31  2020 /usr/local/texlive/2023/texmf-dist/tex/latex/biblatex/blx-case-expl3.sty
Jun 17 12:59 /usr/local/texlive/2023/texmf-dist/tex/latex/l3kernel/expl3.sty
Sep 30  2020 /usr/local/texlive/2023/texmf-dist/tex/platex/base/plexpl3.sty

Three different file names and three different installation dates. I don't
see the error so how do I fix it?

TIA,

Rich