I updated two of my Bookdown projects but found that I was not able to compile the LaTeX. The warning message says:
! LaTeX3 Error: Mismatched LaTeX support files detected.
Loading ’expl3.sty’ aborted!
The L3 Programming layer in the LaTeX format is dated 2020-12-03, but in your TeX tree the files require at least 2020-12-07.
As follows: