In other news, I tried compiling it on a server that runs a recent version of Ubuntu (22.04) and it does compile and seem to compile and link against Qt 5.15.3

Standard and traditional Qt type headaches, where between many different major versions and deprecated stuff and newly introduced APIs between minor versions, compiling and linking software that relies on Qt is a complete crapshoot.

Also, since you don't provide statically linked binary releases or a flatpak or an appimage, you might want to consider making the source dependencies of your software explicit in the Readme (like e.g. the minimum version of Qt5 required, or the qt5Charts dev libs, definitely not something everyone has installed on their computer).