th usual answer is you can not. The way you do it is to create one huge picture, and it will span all your monitors. "there is app for that" and it works pretty good. There is very little customisation, but you can use it from the command line.
install via flatpak, on Ubuntu or Debian
sudo apt-get install flatpak
flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
sudo flatpak install flathub org.gabmus.hydrapaper
run the GUI
flatpak run org.gabmus.hydrapaper or use the CLI
hydrapaper -c path_to_wallpaper1 path_to_wallpaper2 ...
This automatically "builds" the large image for you.