I bought Windowkill in a bundle with Heck Deck with expectation of playing on Linux.

While I can access the Linux version of Heck Deck, I couldn't access the Linux version from either the Itch website or app.

I e-mailed the developer who (a) explained the bundle doesn't include the Linux version (only 2 old Windows versions) of Windowkill but does include the Linux version of Heck Deck and (b) kindly gifted me a copy of the full Windowkill.
I could then see the Linux version of both on the Itch website but still couldn't see in the Itch app (which I wish to use in order to utilise the sandboxing facility).
I bought the game separately in case that was the cause of the problem (and to support the developer). Still the same outcome.

The developer and I e-mailed back and forth a bit more and noticed in the Itch app log that while the Itch app is matching platforms, it sees 3 binaries for 3 platforms for Heck Deck but only 2 binaries for 1 platform to Windowkill -- inline with those allowed by the bundle, not the subsequent gift or purchase.

HeckDeck's log Log-01-HeckDeck-fine.json on lines 18-20, shows it noticing the platforms supported by the different available binaries:

{Windows:all Linux: OSX:}
{Windows: Linux:all OSX:}
{Windows: Linux: OSX:all}

Windowkill's log Log-02-Windowkill-fails.json on lines 19-20, shows it detecting only 2 files, both for Windows:

{Windows:all Linux: OSX:}
{Windows:all Linux: OSX:}

So for whatever reason, I'd say the Itch app still thinks I only have access to the original jam & v2 binaries (provided in the originally bought bundle).

I have since been experimenting with Lutris and see that its Itch integration also only shows the versions from the bundle. From this I conclude the Itch API is only providing the first match for the game, not a merged answer of all licenses. If this is correct, please might it be corrected. If I've misinterpreted or made a mistake in my attempts, do please let me know and I'll happily try other things or provide other information. Many thanks in advance.