The Steam Client Beta has been updated with the following changes: General The Steam client is now 64-bit on Windows 11 and Windows 10 64-bit. Systems running 32-bit versions of Windows will continue receiving updates to the 32-bit Steam client until January 1, 2026. Game Recording Fixed errors copying to clipboard or exporting H265 videos on systems with a NVIDIA 50xx series gpu.
Technically it was just only recently that ms no longer has mainstream support for 32bit oses, as they only dropped that with windows 11.
Makes me think that might be the reason for valve choosing now to do this.