Both of these are super easy to solve without secure boot: The device uses FDE and the key is provided over the network during boot, in the laptop case after the user provides a password. Doing it this way is significantly more secure than using a TPM because the network can stop providing the key as soon as the device is stolen and then the key was never in non-volatile storage anywhere on the device and can't be extracted from a powered off device even with physical access and specialized equipment.
An example of such an implementation, since well before TPMs were commonplace: https://www.recompile.se/mandos
Sounds nice on paper, has issues in practice:
1. no internet (e.g. something like Iran)? Your device is effectively bricked.
2. heavily monitored internet (e.g. China, USA)? It's probably easy enough for the government to snoop your connection metadata and seize the physical server.
3. no security at all against hardware implants / base firmware modification. Secure Boot can cryptographically prove to the OS that your BIOS, your ACPI tables and your bootloader didn't get manipulated.
If your threat model is Iran and you want the device to boot with no internet then you memorize the long passphrase.
> heavily monitored internet (e.g. China, USA)? It's probably easy enough for the government to snoop your connection metadata and seize the physical server.
The server doesn't have to be in their jurisdiction. It can also use FDE itself and then the key for that is stored offline in an undisclosed location.
> no security at all against hardware implants / base firmware modification. Secure Boot can cryptographically prove to the OS that your BIOS, your ACPI tables and your bootloader didn't get manipulated.
If your BIOS or bootloader is compromised then so is your OS.