Lemmy is little too complex for a one click install.
Lemmy consists of:
Lemmy
Lemmy-ui
Postgresql
Pict-rs
Probably something else I’m forgetting.
Each one of those has a number of environmental config options that need to be set before running it all. You need a domain name so that other instances can reach your instance. Your database needs a password, Pict-rs needs to know where to store things, etc.