"Even" Debian?

Debian stable isn't actually as old as some of the "enterprise" distributions: it has a lifetime of about 2 years before being superseded by the next stable release, so even if we pessimistically assume the freeze takes a full year, that's about 3 years from "can have new things" to being superseded. Ubuntu LTS has a similar lifetime, but about a year out of phase with Debian.

The limiting factor for being able to assume new versions are available in the Debian ecosystem is whether you're aiming to support "oldstable" releases that have already been superseded by a newer stable release, but are still supported, like Debian 12 or Ubuntu 22.04 at the time of writing (superseded by Debian 13 and Ubuntu 24.04 respectively, but still supported), or even older LTS releases that have limited or third-party support, like Debian 11 or Ubuntu 20.04. Ubuntu derivatives like Linux Mint and pop!OS are sometimes more of a limiting factor here than Ubuntu itself, because they don't always base their recommended releases on the newest Ubuntu LTS.

Because these older releases have declining-but-nonzero support levels for rather a long time, upstreams will often have to draw a line somewhere, which is a choice based on tradeoffs rather than something with a single correct answer. For example I've found that "newest Debian stable or newest Ubuntu LTS, whichever is older; if your OS is older than this, please upgrade" is a policy that seems to work fairly well in practice.