Nothing really. If you don't want to sacrifice productivity then you go the electron way. Java/Swing has horrible UI/UX and doosen't offer any real benefits on RAM. QT is good if you are willing to pay for the licensing costs for commercial use or you open source your app. Everything else that is cross platform works, until it dosen't. Good luck debugging gtk on windows.

If you can spare the resources, create per platform apps. If not, then electron is your only headache less option.