Cannot run grunt command because of error: cannot find module 'liftoff'
I've faced the same issue under Ubuntu 20.04 and I believe it's caused by several versions of nodejs.
I have installed nodejs 12.16.2 manually (extracted to /usr/local) and that was my mistake. Once I tried to install grunt from Ubuntu package manager it installed nodejs 10.X as a dependency of node-grunt-cli package.
As a result I had the same error message.
The solution was to remove manually installed nodejs and re-install it from package manager.
I also hit this on a clean install on Ubuntu 20.04. I eventually hunted down a recipe at https://ask.openrouteservice.org/t/cannot-find-module-liftoff/1718/5 that seems to fix the problem (not sure why) using nvm to install node v14.16.1, then install grunt-cli globally and grunt locally:
nvm install v14.16.1npm install -g grunt-clinpm install grunt