If you are using aptitude (apt) it is quite simple: https://ubuntu.com/server/docs/how-to/software/automatic-updates/

If you just want security updates and are fine with the default configs:

# apt install unattended-upgrades

Eh, for a toaster it at least makes some sense to have ‘smarts’ for ensuring various types of bread reach the desired crispynes (Lathough none of that needs internet or anything close to 400$ in value). So it would still be more usefull then smart fridge.