@jomoka I’m glad to hear that updating to Focal fixed the Yarn installation issue. Unfortunately, it seems you’ve now run into a dependency mismatch with the Focal’s available installed software.
We have a build image migration guide with general troubleshooting steps for updating build images. It may take a few more builds to figure out, but on the plus side, once you’re building successfully on Focal, you can stay there. The Xenial build image will be scheduled for deprecation in the next few months, so you’ll have a head start on that. Or you can wait for this incident to be resolved, which we’re hoping should happen fairly soon.