They need to have the same TGUI version as you are using. They don't have to build it, you should include the .so files with your application (similar to handling .dll files on windows except that .so files aren't looked for in the current directory and you have to mess around with the rpath of the executable to make it work).
Of course the change that I made will be included in the next tgui release. So once 0.7.4 comes out you could download and use that version. Then you no longer have this special version.
But even after the 0.7.4 release you shouldn't rely on people installing that version manually, you should always try to ship the right dependencies with your application. So in the end it shouldn't matter whether you have a modified or an official version of tgui.
Distributing an application on linux is quite complex and requires a lot of experimentation. If you intend to do so then I suggest you read the following post that I once wrote:
https://en.sfml-dev.org/forums/index.php?topic=20727.msg148895#msg148895Or maybe you can use a different method, e.g. using snaps. Or bundle all the source code including sfml and tgui with a makefile and have it all build on their pc.
But these are things to worry about when the application is finished.