[2019] 2.3.3 won't launch?

I find that occasionally, some anti-virus and firewall software can false-flag updated Stellaris exe as "unrecognized" or a "threat". Try checking it out. Maybe it's been isolated. :)

If you tried that and ran a file integrity check, and it's not helping, just hit up PDX's helpdesk: https://support.paradoxplaza.com/hc/en-us

They usually solve that kind of issues quickly!