Just installed MiKTeX 21.8 on Windows 7 and it will not behave. Running pdflatex from TeXMaker gets me:
This is pdfTeX, Version 3.141592653-2.6-1.40.23 (MiKTeX 21.8) (preloaded format=pdftex 2021.10.8) 8 OCT 2021 14:27
-fmt pdflatex makes no difference.
Needless to say I am unable to compile any documents as it pretends to wholly not understand the LaTeX source:
! Undefined control sequence.\documentclass