Should be build with KF6
Exploring the source code it seems that the client is able to be build with KF6. https://github.com/nextcloud/desktop/blob/master/shell_integration/dolphin/CMakeLists.txt
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Exploring the source code it seems that the client is able to be build with KF6. https://github.com/nextcloud/desktop/blob/master/shell_integration/dolphin/CMakeLists.txt