It seems like you might have encountered a known issue. If your installation was done in the last 2-4 weeks, there's a chance it was affected by a bug in the management companion version that causes it to freeze internally. This issue also occurred with Diederik's setups. To fix this, you can restart the management companion pod using this command:

sudo $(which kubectl) delete pod mgmtcompanion-0 -n mgmtcompanion --kubeconfig /etc/rancher/k3s/k3s.yaml

After restarting the pod, proceed with updating the companion. If your UMH version is significantly older, for instance, one that required downloading a desktop application, this solution might not apply. In that case, you would need to use the new web interface to generate a new command, and then execute that command to install the new companion. Probably need to use the UMH_SKIP_INSTALL=true flag because oyu already have a UMH instance installed, and don't want to overwrite it