Update UI to GTK4 for a More Modern and Intuitive Experience

Dear Solaar Development Team,

Firstly, I would like to thank you for the excellent work you have done in developing and maintaining Solaar. It is an incredibly useful tool for Logitech peripheral users on Linux. I greatly appreciate your efforts and the positive impact you have on the open-source community.

I would like to suggest an update to the graphical interface of the application to make it more modern and aligned with the latest GNOME standards. Transitioning to GTK4 could bring significant improvements in terms of appearance and performance.

Additionally, it would be wonderful if Solaar's UI could be made simpler and more intuitive, similar to the official Logitech software. A minimalist and elegant approach could make the application more pleasant and accessible to users.

I believe these improvements would add great value to the application and would be appreciated by many users.

Thank you for your attention and for your continuous efforts in developing Solaar.

Best regards,

Kong