Error: l.77 \ExplLoaderFileDate{expl3.sty}}

Question

I freshly installed the texlive-full package through synaptic package manager (Ubuntu), and I seem to have some problem with expl3.

Compiling the following document returns a "Missing \begin{document}" error:

\documentclass{article}
\usepackage{nomencl}
\begin{document}
 test 
\end{document}

Log as follows.

This is pdfTeX, Version 3.14159265-2.6-1.40.21 (TeX Live 2020/Debian) (preloaded format=pdflatex 2021.1.19)  19 JAN 2021 12:50
entering extended mode
 restricted \write18 enabled.
 %&-line parsing enabled.
**test
(./test
LaTeX2e <2020-02-02> patch level 5
L3 programming layer <2020-07-17> (/home/fede/texmf/tex/latex/base/article.cls
Document Class: article 2020/04/10 v1.4m Standard LaTeX document class
(/home/fede/texmf/tex/latex/base/size10.clo
File: size10.clo 2020/04/10 v1.4m Standard LaTeX file (size option)
)
\c@part=\count168
\c@section=\count169
\c@subsection=\count170
\c@subsubsection=\count171
\c@paragraph=\count172
\c@subparagraph=\count173
\c@figure=\count174
\c@table=\count175
\abovecaptionskip=\skip47
\belowcaptionskip=\skip48
\bibindent=\dimen134
)
(/home/fede/texmf/tex/latex/nomencl/nomencl.sty
Package: nomencl 2020/12/29 v5.5 Nomenclature package
(/home/fede/texmf/tex/latex/xkeyval/xkeyval.sty
Package: xkeyval 2020/11/20 v2.8 package option processing (HA)
(/home/fede/texmf/tex/generic/xkeyval/xkeyval.tex
(/home/fede/texmf/tex/generic/xkeyval/xkvutils.tex
\XKV@toks=\toks15
\XKV@tempa@toks=\toks16
(/home/fede/texmf/tex/generic/xkeyval/keyval.tex))
\XKV@depth=\count176
File: xkeyval.tex 2014/12/03 v2.7a key=value parser (HA)
))
(/home/fede/texmf/tex/latex/base/ifthen.sty
Package: ifthen 2014/09/29 v1.1c Standard LaTeX ifthen package (DPC)
)
(/home/fede/texmf/tex/latex/koma-script/tocbasic.sty
Package: tocbasic 2020/09/21 v3.32 KOMA-Script package (handling toc-files)
(/home/fede/texmf/tex/latex/koma-script/scrbase.sty
Package: scrbase 2020/09/21 v3.32 KOMA-Script package (KOMA-Script-independent 
basics and keyval usage)
(/home/fede/texmf/tex/latex/koma-script/scrlfile.sty
Package: scrlfile 2020/09/21 v3.32 KOMA-Script package (file load hooks)
(/home/fede/texmf/tex/latex/koma-script/scrlfile-patcholdlatex.sty
Package: scrlfile-patcholdlatex 2020/09/21 v3.32 KOMA-Script package (patching 
old LaTeX kernels)
(/home/fede/texmf/tex/latex/koma-script/scrlogo.sty
Package: scrlogo 2020/09/21 v3.32 KOMA-Script package (logo)
))
(/home/fede/texmf/tex/latex/l3packages/xparse/xparse.sty
(/home/fede/texmf/tex/latex/l3kernel/expl3.sty
Package: expl3 2021-01-09 L3 programming layer (loader)
! LaTeX Error: Missing \begin{document}.
See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...
l.77      \ExplLoaderFileDate{expl3.sty}}
                                         %
? 
! Emergency stop.
 ...
l.77      \ExplLoaderFileDate{expl3.sty}}
                                         %
You're in trouble here.  Try typing  <return>  to proceed.
If that doesn't work, type  X <return>  to quit.
Here is how much of TeX's memory you used:
 758 strings out of 480906
 11450 string characters out of 5910772
 253744 words of memory out of 5000000
 16402 multiletter control sequences out of 15000+600000
 535088 words of font info for 29 fonts, out of 8000000 for 9000
 1141 hyphenation exceptions out of 8191
 63i,0n,54p,234b,36s stack positions out of 5000i,500n,10000p,200000b,80000s
!  ==> Fatal error occurred, no output PDF file produced!

In the example above I used the package nomenclature, but it seems to me that the problem should be somewhere else: I get a bunch of errors if I try to use \NewDocumentCommand or load the package xparse.

This seems to be related with this other question, but that solution (in the comments) did not appear to work for me.

Any idea on what's going on?