How can I save and copy a screenhot at the same time?

The -f is cancelled by the -c:

OPTIONS
   -c, --clipboard
          Send the grab directly to the clipboard.

   -f, --file=FILENAME
          Save screenshot directly to this file.

The file will be stored in memory, not on disk, when -c is used: if you open Libreoffice writer and paste you will see your image.

How can I save and copy a screenshot at the same time?

edit1: bugreport #1446650 but nobody bothered to follow up on this. edit2: I found a way around it by using xclip. Install with ...

sudo apt install xclip

and expand your command with a variable holding date and time and 2 commands:

DATE=`date '+%Y-%m-%d_%H:%M:%S'`
sleep 5 && gnome-screenshot -af $DATE && xclip -selection clipboard -t  image/png -i $DATE