@jfpoulin Its actually pretty easy once you try it, the osd setup is its own tab in betaflight, you'll just have to check boxes from a list on the left of the screen of what you want and they will populate the elements on an example screen for you to arrange. I highly, highly recommend average battery voltage, rssi dbm, and timer 2. Some of my osd are intentionally minimal, but those 3 options are always selected. The artificial horizon helps some as well so you can see if your gyro is calibrated after a crash, as well as the flip over after crash arrow to help with turtle mode, and the G-force meter is always fun to see. For work drones I also include throttle meter, LQ, vtx channel/power, tx power, compass, gps stuff, any available temp sensors, and altitude if the build has a barometer.
On the right hand side of the osd menu in betaflight you can select post flight statistics that will show up when you disarm the drone. Average throttle helps you see if you have a good ratio (low average throttle) and minimum battery voltage will tell you if youre flying your batteries too low. There's a bunch of useful data you can get from post-flight depending on your needs.