Edit: Here's a better example of what I think you would want:
#!/bin/bash
# Often good to assign a numbered parameter to a variable
VER="${1}"
apt install "./${VER}/opensnitch_${VER}_amd64.deb" "./${VER}/python3-opensnitch-ui_${VER}_all.deb"
Also - when debugging bash scripts it's often helpful to just put "echo" before the line you're questioning to see what exactly is being run. e.g.:
That will show the the command that would have run rather than running it, then you can inspect it for errors and even copy/paste it to run it by hand.
Is this installing a local .deb file or installing from a repo? If installing from a repo, the .deb and the full file path are unnecessary. If you're installing a downloaded file, use dpkg -i package.deb not apt.