Projekt Z: Beyond Order is a promising looking upcoming class-based co-op zombie shooter from 314 Arts and we have a fresh short look at it. As far as we know they still plan Linux support which they confirmed to GamingOnLinux multiple times previously.
Inspired by Left 4 Dead, they're hoping to blend "the casual and the hardcore market by implementing a bit of both" they said in an email.
More about it: "Experience the intense action of battling the undead in Projekt Z: Beyond Order, a thrilling first-person zombie shooter with robust character progression and extensive weapon customization. Set around World War II, take on fast-paced missions or explore the terrifying island during expeditions as one of four survivors, each with their own unique abilities and role in 4-player co-op. Shoot, loot, craft, survive."
New trailer below:

Direct Link
I missed it but they also announced back in August that they've moved the release date to sometime in 2026, with no firm date set now. Will keep you posted when I hear more.