[deleted] but I'd like to know when Pixel 4a will stop getting any updates
What kind of updates are you talking about ? The Pixel 4A has already stopped receiving full security updates, it runs Android 13 and will not run Android 14 and above, not appropriately, I still have a Pixel 4a that I only use for Google Pay, it's not a secure device and the phone is off most of the time, it's not relevant at this stage to ask you all these questions, get a recent Pixel when you can and drop the Pixel 4a.
Also, I quote GrapheneOS's comment :
We only officially support the latest version. We temporarily provide legacy extended support releases for devices which only had 3 years of support from launch. This has ended for the Pixel 6 and later with 5 years of support from launch. Pixel 5a will be the last device getting extended support after it's end-of-life and then legacy extended support after the next major OS version is released.
Extended support and legacy extended support cannot provide all security patches due to lack of firmware, driver and other patches. In theory, driver patches could be developed and shipped by others but it's not going to happen in practice. Firmware can't be updated after end-of-life and that's just as important.