I slightly modified your script to: 1. Clean up properly 2. Run spectacle in BG mode, so the window does not pop up after screenshotting.

  #!/bin/bash 
  # Dependencies: tesseract-ocr imagemagick 
  # on gnome: gnome-screenshot 
  # on kde: spectacle
  # on x11: xsel
  # on wayland: wl-clipboard
  
  die(){
    notify-send "$1"
    exit 1
  }
  cleanup(){
    [[ -n $1 ]] && rm -r "$1"
  }
  
  SCR_IMG=$(mktemp -d) || die "failed to take screenshot"
  
  # shellcheck disable=SC2064
  trap "cleanup '$SCR_IMG'" EXIT
  
  #notify-send "Select the area of the text" 
  if  which "spectacle" &> /dev/null
  then
    spectacle -b -r -o "$SCR_IMG/scr.png" || die "failed to take screenshot"
  else
    gnome-screenshot -a -f "$SCR_IMG/scr.png" || die "failed to take screenshot"
  fi
  
  # increase image quality with option -q from default 75 to 100
  mogrify -modulate 100,0 -resize 400% "$SCR_IMG/scr.png"  || die "failed to convert image"
  #should increase detection rate
  
  tesseract "$SCR_IMG/scr.png" "$SCR_IMG/scr" &> /dev/null || die "failed to extract text"
  if [ "$XDG_SESSION_TYPE" == "wayland" ]
  then 
    wl-copy < "$SCR_IMG/scr.txt" || die "failed to copy text to clipboard"
  else
    xsel -b -i  < "$SCR_IMG/scr.txt" || die "failed to copy text to clipboard"
  fi
  notify-send "Text extracted"
  exit