Hi this just worked recently for another user: Missing all new apps
You can first try the normal fix is SSH and run command:
cd ~umbrel
sudo scripts/repo update
After waiting ~5 minutes after a reboot it should also update,
You can move on to trying the delete lock file command and let us know if that works:
sudo rm -f /home/umbrel/umbrel/repos/https---github-com-getumbrel-umbrel-apps-git/.git/index.lock
Can reference How to SSH into Umbrel here: Official Umbrel Troubleshooting Guide and FAQ