Which fast-loading (without unnecessary images and text) single-board computer for a Qt program should I choose?

Question

Iron

I choose a single-board computer for running the program on Qt that meets the following requirements:
- 12V power supply (preferably)
- The presence of more or less ready-made OS assemblies (if not X86. If X86, then TinyCoreLinux is fine with me)
- High download speed
- No manufacturer's advertising and any other information before loading the OS (ideally, the ability to install your own logo)
- Availability of RS-232 (highly desirable)
- Passive cooling
What would you advise to choose?

Answer 1

I suggest Raspberry PI) it loads quickly, you can easily buy a switching power supply with 12> 5, there is no manufacturer’s advertising, there is a rainbow test picture when loading the bootloader, it’s not easy to turn it off
. Then Linux loads and it’s just as easy to cover the boot log with your picture.
RS232 is available on the GPIO 14/15 board or you can connect a USB adapter.
Cooling itself is passive.