cowboy420 I solved this issue for myself today. I was running Ubuntu 18.04 and I was encountering this error also. I think WordOps no longer supports those versions of Ubuntu, or at least the packages installed on older versions. Ultimately I was able to fix this error via upgrading my server to Ubuntu 20.04, reinstalling WordOps and then doing the stack upgrades. I would say make sure you 100% have a backup and a plan in place to rebuild the server if things go poorly but it worked flawlessly for me.
I started by doing the release upgrade via the "do-release-upgrade" command. This upgrade took a long time, I excepted default options here and always chose to keep the current config if asked. It asks to reboot and I did that and it continues until faced with a login.
After login I ran the WordOps install command "wget -qO wo wops.cc && sudo bash wo"
Then,
wo stack upgrade
then
wo maintenance
After that everything works as designed on the latest version of WordOps. The sites are still all running on whatever version of php they last were using so those may have to be updated for security and performance reasons.
Hope that helps you or someone facing this issue. I do realize this solution could be an issue for people with limited server resources.