Fairphone 4 (fairphone-fp4)
Users owning this device
How to enter flash mode
For booting into fastboot, turn off the phone, hold volume down and plug in the USB cable.
Unlock the bootloader as described on the Fairphone Support page.
You also need to erase the dtbo partition for the current slot with
fastboot erase dtbo when using the mainline kernel.
The rest of the installation is pretty standard, but as the device has A/B slots you have to watch out for the correct slot being active.