It's seriously been delayed by about a month.
Serious Sam 4

Originally set to release in August 2020, Serious Sam 4 will now be released on September 24, 2020. It's not a massive delay, but it is one that was worth bringing to the attention of fans. It is in September when Croteam and Devolver Digital will release the game on PC via Steam and through Google Stadia. Oh yeah, Stadia is still a thing.

If you want, you can pre-purchase Serious Sam 4 right now through Steam. It's priced at just $39.99 (USD).

Humanity is under siege as the full force of Mental’s horde spreads across the world, ravaging what remains of a broken and beaten civilization. The last remaining resistance to the invasion is the Earth Defense Force led by Sam “Serious” Stone and his heavily-armed squad of misfit commandos.