[2023] How do i make this game into the zombie survival game?

The game has to be more clever than just adding more zombies, because each zombie has a performance cost. Turning on feral sense is a good start, because then you will more easily aggro the zombies that are already there but weren’t going after you. You will also face more challenge from zombies with a higher gamestage: either directly by leveling up your character, or due to gamestage multipliers like being in a more dangerous biome. As for Blood Moons, you set how frequent they are. You can have a Blood Moon every night if you want. Lastly, there are screamers. Some players will deliberately raise the activity in a small area, for instance by running many forges, to draw the attention of screamers, and then purposefully let them call in hordes.

It sounds like wandering hordes are closest to what the OP is after. I imagine a mod could pump those up separate from biome zombies.