https://help.steampowered.com/en/faqs/view/4784-4F2B-1321-800A#:~:text=Steam%20Support%20%3A%3A%20Windows%207%20and%20Windows%208%20Support&text=As%20of%20January%201%202024,on%20those%20versions%20of%20Windows.
"As of January 1 2024, Steam will officially stop supporting the Windows 7, Windows 8 and Windows 8.1 operating systems. After that date, the Steam Client will no longer run on those versions of Windows."
More importantly - "In order to continue running Steam and any games or other products purchased through Steam, users will need to update to a more recent version of Windows."
@CifrareVerba It is Microsoft who needs to support Windows. If it was Linux, then you could blame Valve for not supporting Linux anymore. That happens, because Windows is closed source.