Illinois's new law requires operating system providers to add age verification by 2028 including open-source projects
(gov-pritzker-newsroom.prezly.com)
From page 7 of the bill:
"Operating system provider" means a commercial or non-profit entity that controls the Internet-enabled device's operating system, including the design, programming, or supply of operating systems for the Internet-enabled devices.
So it does appear Linux and other open source OSes would be included.