complain to the hdmi forum, it is their fault that its max 4k@60hz on linux (at least for amd gpus, intel arc has a dp to hdmi converter chip on their cards) https://www.phoronix.com/news/HDMI-2.1-OSS-Rejected
One of the limitations of AMD's open-source Linux graphics driver has been the inability to implement HDMI 2.1+ functionality on the basis of legal requirements by the HDMI Forum
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