When start new world, there is no enemy on the map?

It's likely caused by RSO settings. Please refer to mod-compatiblity doc for details.
https://github.com/heyqule/enemy_race_manager/blob/main/Mod-Compatibility.md

Warning: Not recommend to apply to an existing save with Factorio World

As map-gen-scale minimum value raise to 10, this will skew the map generation of existing map. The mod also force Factorio World to only generated on planet earth. It can no longer generate on planet Nauvis.

I don't see Red Army unit on Nauvis. There is only biters. Why?

ERM 2.0 does not change nauvis enemy by default. You can change the nauvis enemy generation to mixed / 2ways / 4ways in start up setting.