@tomsome
Yes, the developer mode think is for Android users.
If you already have Ubuntu Touch, then this is already done as well as unlocking the bootloader (expect if you locked it back despite it being deprecated).

I've been using UT 20.04 on my OnePlus 6 without issues, including Waydroid with MicroG. However, today I noticed there's no audio from the headphone jack to my stereo system. Bluetooth audio works fine with a Bluetooth speaker.