Steam recently announced that after February of 2024 they’ll no longer support Mojave (a 5 year old OS) and older versions of MacOS, which Apple no longer even supports with security updates. The dropped support is due to Chrome dropping support for those OS versions, and Steam relies on Chrome for some of its functionality. The lack of support also doesn’t mean Steam will suddenly stop working, simply that they are no longer going to provide updates or customer service for it. This impacts 2% of Steam customers with Macs - meaning roughly 0.03% of Steam’s customers, or around 46,000 people.
Just to be clear, is that what you’re talking about?