How does the GPL work when releasing embedded (embedded/IoT) hardware?

Question

Licenses for software and other works

Greetings!
I do not quite understand how the GPL and Apache licenses should be applied if the hardware is the commodity and the software is not separately supplied, and products with open licenses are used in the development of the firmware. In what case should I undertake to provide the source code to the end user? There are two main options:
1. RTOS is used under an open license, the rest is written independently.
2. The library is used under an open license, the rest is written independently under bare metal.
Of course, I don't want to publish my own written code.
Thank you in advance for your answers and for refraining from shouting "you can't take without giving in return" :)

Answer 1

In short - read (preferably English, Russian translations have no legal force) the texts of all licenses, everything is written in detail there.
Apache is a very free license, there will be no problems with it.
If you use the Linux kernel in your product, you should allow the user to unlock the bootloader - everything is like with androids.
Number two - no good if the library is under the GPL. You may not, under the terms of the GPL, link your proprietary product to GPL code.
This does not mean that it (your proprietary code) cannot be run on Linux, but, for example, the GPL itself (until you publish the code) prohibits you from using the GSL library that comes under GNU in it.
Look for libraries with the LGPL license, you can link with them and not publish the source.