I feel that at the very least, the customer in that case should be entitled to a complete refund of the product, regardless of whether they bought it 5 days or 5 years ago and regardless of the condition their device is in.
This should at least give some incentive to companies to not perform such sweeping changes to their terms of service and if they do, the customer can more easily remove themselves from the lock-in without taking a financial hit.
The easiest way to block an auto-upgrade to Win11 is to just disable TPM in the BIOS. That way Windows will see the PC as not Win11 compatible and not perform the upgrade.