Had a similar issue with fairphone where it was not recognized when in fastboot mode everytime I plugged in.
Basically my computer (Windows 11) requires to manually install the driver of my phone identified as “unknown device” in device manager. Had to download the google usb driver → device manager → Unknown device → install driver from file → adb interface
Funny enough, when I switched to recovery mode I actually had the popup of USB drivers being installed automatically, if I remember correctly. But after this, things still didn’t work. But this is a good idea, where to check for the problem, too. Thanks!
OK, using Linux Mint. No experience with Windows, sorry
Hello
Maybe the popup in the phone, “allow USB debubugging” ? 
I also had to a few times after booting, no matter what mode.
Even if the cable is pulled, confirm again and again, device / PC remember the phone is not interested. 
Is this not normal behaviour and only fastboot commands would work? And would you not need to update the driver while in fastboot? On the FP2 and FP3 driver issues are most times fixed by actively searching for updates und er Windows updater while the FP is connected in fastboot. Under additional updates - driver you might find google stuff to update
Hello
No, you start adb reboot etc and switch to fastboot flashing etc. 
I guess it doesn’t work for /e/. Not for me anyway and I’m not alone with this.
And maybe someone can push this all together
so you are telling me when you are in the bootloader /fastboot mode through adb reboot bootloader, you can use adb commands? I cannot neither on the FP2 nor the FP3.
Eithter way I think when the above reported issue is really caused by missing drivers, it does not really matter. In addition I doubt that your issue is the same as reported in the other post else hirnsushi would have had a solution. In the other post the issue is that the bootloader is locked and OEM unlocking is disabled and phone not booting, so no way to enable OEM unlocking again and without that the bootloader cannot be unlocked again.
I guess because ADB and fastboot get distributed together they often get lumped together as simply ADB.
When we get into detail, the two are seperate entities working with different modes of the phone, and referring to fastboot as ADB then leads to confusion in troubleshooting.
I think we should assume fastboot doesn’t find the device.
Thanks for all the answers. I managed to install /e/ using my old Win7 pc with a usb-cable I bought with the FP4.
Hello
Waiting for any device,… unauthorized,… I also had the messages/ errors and was also stuck in fastboot mode. Just wanted to “try” to explain how I solved it.
Good luck 
https://forum.fairphone.com/t/trapped-in-fastboot-mode-with-locked-bootloader-and-corrupted-e-os/80985/16 seems to be more difficult to solve because we need a way to enable “oem unlocking” without a working OS/recovery
Es ist ja bereits bekannt dass einige Apps nicht laufen. Osmand, Aegis, etc… Das ist auf die geringe jvm heapsize zurück zu führen.
Ein issue ist in Git eingekippt, bekannt und bereits gelöst. Kommt mit dem nächsten Update.
Workaround für die, die nicht zum Update warten können: im /e/ Forum eben berichtet und von mir bereits getestet. Funktioniert. Danach läuft Osmand, davor nicht.
Test Option: *#*#2886#*#* is no longer working wih /e/
Is there an alternativ, or is it not possible on /e/ (Lineage, CustomRom) in general?
It’s the same at least with the respective test menu dial code for the Fairphone 3/3+ in /e/OS. I wouldn’t get my hopes up.
Maybe @urs_lesse found at least a solution for some the tests. The Fairphone Checkup App (Originally for the FP2) fork available on F-Droid seem to work on other phones as well
In vanilla FPOS it’s called MMITest. It should show up under Settings → Apps if Show System is active (or check it with adb shell pm list packages mmi).
If it’s there you can trigger it with
$ adb shell am start-activity -n com.android.mmi/.MMITestMain
Edit: I checked the /e/ images, it’s not included.
I had same problem. I tried with diffferent cables, with no luck. I also try to force reinstall of the driver from the devices manager. No luck either.
I finally solved the problem with a simple “windows update”. But I had to go in “the optionnal updates” part. There I found updates waiting for Android.
M.
Yep, that’s the most frequent issue on Windows
You have to install ADB & fastboot drivers in the Windows Update section “Optional updates”
I remember they detailed the procedure for FP3 afaik, but nothing for the FP4
That’s it with W11, if it can help someone:
For the last one, you can check only the ones that are related with ADB (Android Debug Bridge) and fastboot
However, I advise you to do all the updates, these are frequently drivers updates
Also, I have found quite a few bugs on /e/OS:
), but you have to:
)Apart that, everything seems to work well for me, with Lawnchair 2 (got it from Aurora store, cause the stock launcher is horrible) and Magisk root (I’ll make a wiki on how to do it in a few days )
