Qt (C++ + QML, python + QML or even C++ + QtWidgets) is well suited for desktop application development. You can easily stay with the open source licence of Qt. The Qt website is not really clear about this and they will push you to go for a commercial licence.
Electron (+ any web front-end UI framework, like React) will also do the job.
You can also check for Java Swing or Java Jetpack Compose.
Wonderful promise ! I'm really thinking that I need an app like that one but how to justify the price ? I'm ready to pay for that kind of service but it's seems too expensive to me. How an app like this can cost you 10$ per month and in comparison an app like Procreate (best drawing app on iPad) cost you only 10$ (not per month or year, just 10$).