For a washing machine or refrigerator, I’d say twenty years is the minimum. For a phone or computer? I’d say at the very least five, but preferably ten years from the last sale of a new, used, or refurbished device sold by them or their authorized resellers. Require security updates for at least twice as long, or when the manufacturer can prove all devices are out of use.
There should be a standard for replaceable boards for major appliances. Compressors in fridges and motors in washers ultimately do not change. The front interface changes but that's ultimately just programming the on/off cycle for that motor.
For a washing machine or refrigerator, I’d say twenty years is the minimum. For a phone or computer? I’d say at the very least five, but preferably ten years from the last sale of a new, used, or refurbished device sold by them or their authorized resellers. Require security updates for at least twice as long, or when the manufacturer can prove all devices are out of use.