emacs-auctex refuses to open .tex-files

Question

After installing emacs 28.1 and auctex 13.1 I can't open .tex-files any longer.

If I enter in emacs Ctrl-x -f Blau-2022-03-20.tex I get

 Debugger entered--Lisp error: (wrong-type-argument arrayp nil)
 replace-regexp-in-string("\[ \\11\\15\\n%\]" "" nil)
 LaTeX-xparse-macro-parse(mac)
 LaTeX-xparse-auto-cleanup()
 run-hooks(TeX-auto-cleanup-hook)
 TeX-auto-parse()
 run-hooks(TeX-update-style-hook)
 TeX-update-style(t)
 
 #f(compiled-function () #\<bytecode -0x12260f12797895d8\>)()
 run-hooks(find-file-hook)
 after-find-file(nil t)
 find-file-noselect-1(#\<buffer Blau-2022-03-20.tex\> "\~/Desktop/Eigene Dokumente/Briefe/Blau-    2022-03-20...." nil nil "\~/Desktop/Eigene Dokumente/Briefe/Blau-2022-03-20...." (790801 2051))
 find-file-noselect("\~/Desktop/Eigene Dokumente/Briefe/Blau-2022-03-20...." nil nil t)
 find-file("\~/Desktop/Eigene Dokumente/Briefe/Blau-2022-03-20...." t)
 funcall-interactively(find-file "\~/Desktop/Eigene Dokumente/Briefe/Blau-2022-03-20...." t)
 call-interactively(find-file nil nil)
 command-execute(find-file)

an can't open the file at all. If I click on the four dots, .tex appears.

BTW: It works with .tex~-files.

I have no idea what I could try, it worked for decades...

The question has been asked since 2014, but all solutions I found didn't work for me.

PS: It works if I enter myfile.tex for a second time. So after Ctr-x -f myfile.tex I get the strange message, but after another Ctr-x -f myfile.tex I can open the file as usual.