I am also seeing the same symptoms as reported by OP,
- fresh install of KDE NEON 5.14 (based on Ubuntu 18.04) - using gtk3 app Tilix, i do not see the cursor change to allow me to adjust the app size
and the workaround (ALT + right click to resize) works for me
I am also seeing the same symptoms as reported by OP,
- fresh install of KDE NEON 5.14 (based on Ubuntu 18.04)
- using gtk3 app Tilix, i do not see the cursor change to allow me to adjust the app size
and the workaround (ALT + right click to resize) works for me