In the directory named .ddev/commands/host, create a file named launch-uli.sh using the following content:
launch-uli.sh:
#!/bin/bash
## Description: Launch a browser with admin login from drush uli
## Usage: launch-uli
## Example: "ddev launch-uli"
open $(ddev drush uli)
Note: Change open to the appropriate command for your OS. .ddev/commands/host/launch has examples.