ReactOS is an open source operating system that recreates binary executable compatibility with Microsoft Windows, and as part of an effort to support UEFI with ReactOS, a development version of ReactOS is already running on Valve's SteamDeck handheld gaming console.
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Since ReactOS's binary compatibility with modern Windows games is still quite limited, and support for Windows device drivers in particular is spotty, it's not yet suitable for use with any big games!
ReactOS has been working on UEFI support for several months, which you can track via this pull request:
https://github.com/reactos/reactos/pull/5267
The developers of ReactOS shared that one of them ran ReactOS on an AMD-powered SteamDeck using the code in development:
This might not be entirely practical at this stage, given ReactOS's limited compatibility with device drivers and modern game executables, but it's an interesting milestone for this open source project.