No, the Big Sur support for older hardware is the same now as it was in June when it was publicly released. The only temporary change is two models are temporarily blocked from starting an update - https://mrmacintosh.com/big-sur-11-0-1-20b50-released-to-block-install-for-2013-14-13-mbpros/ but your model should be good to go for restores and installations.
What does and now it's not working! mean precisely?
Now, older hardware goes out of support all the time based on the age of purchase and has nothing to do with whether the gear runs the new OS. Either way, if you want to ask a follow on question for your specific symptom, we may have help for that whether it’s out of “official support or not, but hopefully this answers how Apple will support you.
There was a time window when Big Sur Upgrade didn’t check for disk space properly and you could get stuck if you didn’t have about 35 GB free space or more.
- Big Sur 11.3 Beta – Confirmed
- Big Sur 11.2 – Confirmed
- Big Sur 11.1 – Not affected
- Big Sur 11.0.1 – Not affected
As long as you start from a newer installer, this issue should be fixed now.