Forge: copy existing server with old specs

Hi there, I need to create a replica of an existing server to use it as staging environment.

The problem is that this droplet was created years ago with Ubuntu 18.4, which is not available anymore when creating a new server, and I need all the system configuration to be the same.

I can duplicate the droplet in Digital Ocean, but then I don't see a way to connect it to Forge afterwards.

What do you suggest?