Eternity has a data saver mode

No, that's a different protocol, the tearing patches, already merged, but i believe we're still waiting on some patches to the kernel to get them fully working(i think it was kernel 6.8 that had them), Nvidia's drivers also need to add support for it, they've given no timeline for that so far however

https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/65

That blogpost is considered to be somewhat flawed with its information, as explained here: https://tesk.page/2021/02/11/response-to-flatkill-org/