After Update Installation the File Format Language highlighting seems to be inactive
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 Found no (new) option to possibly reactivate the (automatic) file format language dependent highlighting. Update installed today: Debug info 
 Notepad++ v8.4.8 (64-bit)
 Build time : Dec 24 2022 - 19:40:27
 Path : C:\Program Files\Notepad++\notepad++.exe
 Command Line : “C:\Program Files\Notepad++\change.log”
 Admin mode : OFF
 Local Conf mode : OFF
 Cloud Config : OFF
 OS Name : Windows 10 Enterprise (64-bit)
 OS Version : 21H2
 OS Build : 19044.2486
 Current ANSI codepage : 1252
 Plugins :
 mimeTools (2.9)
 NppConverter (4.5)
 NppExport (0.4)
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 Automatic filetype detection works for me. My first guess is that you have a file greater than 200MB, because there is a set of options (added in v8.4.7) called Settings > Preferences > Performance which allows you to turn off certain higher-CPU-cost features of Notepad++ for large files, and syntax highlighting is turned off by default for files >200MB.