I don't want to have to specify a number of days or episodes to keep. Instead, I want to keep as many episodes as possible while keeping a specific amount of storage space free on the device.

So I want Podcast Addict to continuously download new episodes and not delete old episodes until less than 2 GB of space is left on the device. If less than 2GB of space is remaining, then delete as many old episodes as necessary to make at least 2GB of space free.