Strictly speaking you don’t have to. “There’s more than one way to do it” is a good saying here 
Renaming the file to “recovery.img” would adjust the file name to the command. But you could as well adjust the command to match the file name:
fastboot flash recovery recovery-e-0.14-q-2021012698290-dev-GS290.img
On second read I sense a small misunderstanding.
The instructions mention “this is in your home directory”. A user’s home directory typically is /home/<username>. So /home is jut the base path under which all user home directories are stored (if you had multiple user accounts on your computer there would be multiple “home directories” beneath /home.
In your case, as you user name is gdk, your home directory is /home/gdk. “outside” of your home directory you typically don’t have write access. That’s why you couldn’t move the folder to /home/platform-tools (that’s what I understand you meant by “i couldnt copy the folder to /home”).
Some more explanation is here: https://en.wikipedia.org/wiki/Home_directory
ah okay. i thought maybe the system or program … needs the file to be named recovery.img for some reasons later.
ah ok. yeah, on second thought it makes sense with the home folder
thanks
i don’t know if it’s still useful, however i managed to get back stock 2 times and lock bootloader 2 times.
You need to flash the stock rom provided here :
https://doc.e.foundation/devices/GS290/install#before-flashing
(* Download Android 10 firmware
only if reverting to Stock ROM)
reverting with sp flash tool (pay attention to the preloader, untick !!!)
turn on again, then regain debug permissione and usb file transfer mode
adb reboot bootloader to enter fastboot mode (or power key and volume up)
in fastboot mode run fastboot flashing lock
volume up to accept
reboot.
If I understand you correctly, you locked the bootloader after you installed the stock rom again. So without /e/os. Did I understand that correctly?
But I want to know how I can lock the bootloader again after I successfully complete the installation of /e/os.
A friend of mine has successfully flashed the fairphone 4 with /e/os and according to the instructions (Install /e/ on a Fairphone FP4 - “FP4”) locked the bootloader again after completing the installation.
Why does this still not work with the gigaset gs290?!