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PC Gamers Abandoning Windows 11 for Linux with Higher FPS & Fewer Interruptions
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I'd assume that for the majority of his career he was using something like Series 20 OS (Nokia's proprietary OS) or the BlackBerry OS (before it was rewritten to be based on UNIX-like QNX).
But since then, yeah. There are literally no other options since MS killed Windows Mobile with prejudice.