Other answers provided here did not help (looking for registry entries pointing to missing office exe files in HKCR\TypeLib, reinstalling Office, embedding the interop assembly in the application either via COM or Nuget, changing build from x86 to x64).

Running process monitor, filtering for my application exe and errors, it was showing a lot of PATH NOT FOUND errors looking for vbe6ext.olb. I found it in

C:\Program Files\Microsoft Office\root\vfs\ProgramFilesCommonX86\Microsoft Shared\VBA\VBA6

I copied it to C:\Windows\System32 (one of the locations where Process Monitor was showing that the app was looking for this file), and this resolved the issue for me.

Register the type library using regtlibv12.exe would probably be an even more precise solution, but the above was enough for my app to work again.

Note: for 32-bit apps on 64-bit Windows, the correct folder to copy it would be SysWOW64.