The following will check the Linux Vivaldi (and Chromium) version installed, withouit having to start it up:
grep -Pao 'Chrome/.Vivaldi(.([0-9]+\.){3}[0-9]+){2}' /opt/vivaldi-snapshot/vivaldi-bin | sed -r 's,.*(([0-9]+\.){3}[0-9]+).(([0-9]+\.){3}[0-9]+).*,Vivaldi: \1\nChromium: \3,'
Note: This requires GNU grep compiled with support for Perl regular expressions.
Here is a less fancy version (without the helpful formatting):
strings /opt/vivaldi-snapshot/vivaldi-bin | grep -xA3 Chrome/