On the system software side, the mostly tacit/occasionally explicit reminder by Apple is they support the current OS and the prior two major versions of OS builds, before dropping them. As of this writing, Ventura is current, so Monterey and Big Sur are what Apple are supporting with software, firmware, and security updates.
*
This has been the case since at least when Snow Leopard was the current OS (and the oldest Apple supported was Tiger). The obvious issue here is, starting from Lion (the first version of OS X/macOS to be overseen completely by Tim Cook
**), Apple began rolling out their major version OS builds on a strictly annual basis, regardless of how “finished” that major version was.
And Apple could do this because consumers were no longer buying the OS and, as consumers should, expecting the OS product to be a finished quality product becoming of a purchased product. That’s because the consumers who once bought the OS stopped being treated by Apple as consumers and were re-designated b the company (and backed by shareholders) as
being the product. This is evidenced by the significant telemetry and umbilical corded-nature of what OS X/macOS became from Lion, forward, which has only escalated with each new major version since.
Consequently, building and releasing a relatively tidy product, the OS, stopped being the priority since consumers no longer could consume it via purchase of an upgrade. As the OS’s tidiness was also deprecated, so too was the imperative to keep the OS free of guff and garbage development contents, such as the inexplicable appearance of the Bitcoin manifesto, post-High Sierra, and other contents which bear no relationship or purpose for the end-user (i.e., the “former consumer”, now the “current product”).
* This typically gets treated separately from hardware-specific fixes which need addressing, as
Apple’s hardware support is dependent on whether a product is designated as either “supported”, “vintage” or “obsolete”. This often goes back as far as seven or eight years for particular Macs, and less so for others. So long as a product is in “vintage” status, there is still the possibility of a fix being released for something to come up in particular — often matters pertaining to things like component firmware.
** Yes, I completely have a bee in my bonnet about Tim Cook, and yes, this bee is living in my bonnet forever