Fusion is part of Qt and the default style in Qt, nothing specific to Strawberry. For any application which doesn't have a setting to change style you can still set this by using the QT_STYLE_OVERRIDE environment variable.
But maybe you didn't have this issue with Clementine because you either used a different style, or there is a bug in the newer versions of Qt. The latest release of Clementine is still using Qt 4 (although you can build Clementine with Qt 5 with the latest source code from git). While Strawberry is Qt 6, but still compatible with Qt 5. Qt 5 is more or less end of life from Qt for open source use, the Qt company have closed the Qt 5 branches.