Ideal language and framework for legacy Windows (XP) and modern Linux

I'm looking to write a simple program which can run both on Win XP SP3 (ideally without added dependencies, if it all possible) and modern Linux. Really, it should be platform agnostic but XP and Linux are what I'm specifically interested in.

The program will be for managing my cd-keys for my XP games. It'll have a simple gui with a search box and an output box. It'll parse text files in it's subdir when searching via search box and output the cd-key string contained within.

From what I can see, it would be good/viable to use C++ so it runs on XP and Linux and use gtkmm3 for the UI for the same reason.

Does this make sense or am I missing something glaringly obvious? Any input would be much appreciated~