Grass/no grass makes no difference (especially in the biomes that lack grass)..

Spawning logic:
https://valheim.fandom.com/wiki/Spawn_zones
Base items that prevent spawning.
https://valheim.fandom.com/wiki/Player_base

Just a note it may be a bug or it may be intentional but deer and birds can spawn in even if your base has complete anti-spawn coverage.
https://steamcommunity.com/sharedfiles/filedetails/?id=2920176358
https://steamcommunity.com/sharedfiles/filedetails/?id=2860289081