This xbar plugin let's you update formulae and casks.
Download and install the plugin:
mkdir "~/Library/Application Support/xbar/plugins/homebrew-update"
wget -qO- https://github.com/mietzen/xbar-homebrew-update-plugin/archive/refs/heads/main.tar.gz | tar xvz -C "~/Library/Application Support/xbar/plugins/homebrew-update" --strip-components=1
ln -s "~/Library/Application Support/xbar/plugins/homebrew-update/homebrew-update.1h.sh" "~/Library/Application Support/xbar/plugins/homebrew-update.1h.sh"
If you click on a formula or cask a Terminal opens to upgrade the specific formula or cask. You can also click on Upgrade All to update all listed formulae and casks.