I've created an SDL2 application that has high DPI support and displays correctly when running the compiled binary manually.
I've created a .app structure (Info.plist, Contents/..., etc...) with the compiled binary inside. The app itself launches and runs fine, the problem is that despite adding NSHighResolutionCapable to my Info.plist the window is presented with a low DPI, contrasting the DPI when launching the compiled binary without the app structure. The Get Info menu displays the Open in Low Resolution option as ticked and greyed out, I have not touched this option.
Unless there are further steps for macOS app packages required, I can confirm that there is nothing wrong with the binary itself as it runs at high DPI when ran manually.
Below is a snippet of my Info.plist, I've redacted
a chunk of irrelevant keys for readability sake.
[...]
<key>CFBundlePackageType</key>
<string>APPL</string>
<key>CFBundleShortVersionString</key>
<string>1.0.0</string>
<key>CFBundleVersion</key>
<string>1.0.0</string>
<key>NSHighResolutionCapable</key>
<true/>
What changes should do I need to make for running at high DPI?
I was lead in the right direction by TheNextman, it was the simple issue that a previous version of the Info.plist was cached before I added the high DPI key.
To update the cache I entered the command /System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -f [path to .app] as explained here.