Configure on Cinnamon X11

1. Open System Settings > Keyboard, you can use search method to find it.

2. Move to Layouts tab and Click on Add which will then open a new tiny window, where search for "openbangla" and Select "Bangla (OpenBangla Keyboard)", input method "IBus".

3. As written below, you can switch to next layout with Super + Space, or configure to whatever you prefer.