Labris

Did some more testing and found workaround. Newest MC and Forge for it didn't have this problem, also isolated that problem is only with fullscreen, meaning there is problem with exclusive fullscreen handling when application gets moved to background/minimized. So installing this mod fixed problem for MC 1.12.2 and forge for it https://www.curseforge.com/minecraft/mc-mods/fullscreen-windowed-borderless-for-minecraft

Tested with 5900X, 64GB 3200 MHz, 3070 Ti, driver 551.86 Edit: Win 11 Pro, MC allocation limit 16GB GPU clock range: 200 - 1950 MHz, usually 210 MHz with 10-30% utilisation on desktop idle use Render settings: Vsync ON, Framerate unlimited, Render distance 32, Fullscreen ON (60hz monitor, so 60 fps with vsync) Vanilla minecraft: Main menu: 210mhz idle clock always, ingame clock around 400 - 1000 mhz with ~30% utilisation and after alt+tab stays at same. Modded install with curseforge app, only said forge added: Main menu: 210 mhz idle clock always, ingame clock around 400 - 1000 mhz with ~30% utilisation, but after alt+tab gpu clock shoots up to 1950 mhz and utilisation is at 50-60% After disabling all render and chunk related stuff in config, after alt+tab it goes up to 1500 mhz. So game turns gpu into space heater when its not even seen. GPU usage returns to expected when game comes back on top. If instead of unlimited fps, fps is set to ~60, then during alt+tab gpu stays at same range as vanilla, but minecraft has horrible limit logic and framerate limit causes lot of tearing, so its not an option. So it seems that when alt+tabbing, for some reason logic no longer takes vsync toggle into account. So expected behaviour would be for it to work like vanilla does. keep rendering in same manner, no matter if its seen and use same amount of resources. Essentially noticed this behaviour while playing Supersymmetry and after elimination testing, result was that only Forge was enough to cause it. And also confirmed it by doing fresh pack with only Forge added, so no other mods even in disabled state. Also happened with both singleplayer and remote multiplayer. Other offender was "Universal Tweaks" which introduced same effect to main menu with its # Removes the hardcoded 30 FPS limit in screens like the main menu B:"Uncap FPS"=true setting, meaning when game was on top, it still worked in limits of vsync cap, but after alt+tabbing even in main menu gpu usage shot up to max.