Of course, this is not only about Ubuntu, Fedora, or Linux Mint, as it would apply to all GNU/Linux distributions, desktop environments, and application hubs lke Flathub or Snap Store, which will have to comply with the upcoming law in the near future in some way, especially since similar laws have already been proposed in other US states, including New York and Colorado.
If systemd pushes age-gating at the init level, that’ll be basically all distros, then, except for maybe the alt-init ones. No, even Arch wouldn’t be spared from this.