"No Fairphone 4 found in fastboot mode" error message

My reply before coffee

Absolutely … Install fastboot drivers.

… and

made me think of

  • Caution: The default adb installation on OS like Ubuntu can be outdated and can cause errors. We would recommend that linux distribution users ensure they use the installation process given here … and
  • is “add the path to your PC configuration” done correctly … from
  • Installing adb and fastboot on a Linux PC

EDIT … but, to satisfy yourself and especially when asking for help always

fastboot devices

at any change you make and show the result if / when you ask again.

However you did manage to unlock … please confirm this

In light of


You also say

Well which … or both (??) … it will help if you show your actual output.

I would suggest that it is not a good way forward to attempt to start the script again if you cannot immediately before get the device to self identify with

fastboot devices

You might possibly have a variation of this Flashing script wrongfully claims the phone is still locked - #15 by Maryn which was part of my thinking behind having adb / fastboot correctly installed.