@Alex-Woolf,
As @Claudia-Frank said, “Same applies to UDL”, and she said earlier that the custom syntax highlighting settings, which are known UDLs (User Defined Languages: Language > Define Your Language) are stored in userDefineLang.xml. You could either copy that single file to the new PC, or you could use the UDL window’s interface:
Original PC: Language > Define Your Language
Use the pulldown to select the User Language: ____ you want to transfer, and click the Export... button
Copy that file on the new PC
New PC: Language > Define Your Language: click the Import... button, and select that file
Repeat for every UDL (syntax highlighting definition) that you want to transfer.
If you’ve got more than one, it’s probably simplest to just copy the whole file, but if you only have one, or you don’t want to duplicate them all, you can do it using the UDL window.
BTW: Since it wasn’t mentioned, those files are by default in %AppData%\Notepad++\, though if you’ve got a portable version of NPP, or if you chose to not use %AppData% when installing, they will be in the same folder as your notepad++.exe.