mrubyc VS Metasploit

Depends on what you mean by embedded? Microcontrollers (AVG/Arduino)? System-on-a-Chip (SoC)? Embedded Linux system (Raspberry Pi, ARM/MIPS, etc)? There is mrubyc which has been put onto various embedded systems. However, if you want raw performance and minimal memory usage, C is probably still the best option; although it is notoriously difficult to write secure code in C, which is why Rust and Zig are becoming popular for embedded development.

Ruby is mainly used in web app development because that's what makes money. However, Ruby is also used in Information Security (infosec) and there are a dozen or so Ruby security tools and libraries (metasploit, ronin, arachni, dnscat2, dradis). There's also SciRuby which aims to allow Ruby being used in the scientific/academic fields. You've probably heard/seen DragonRuby which is helping to popularize Ruby for simple game development. There's also a lot of interesting work happening around mruby and mruby-c (see mruby/c on Flipper Zero and mruby on DreamCast).

Metasploit

Metasploit: https://github.com/rapid7/metasploit-framework

1-) Learn Hacking on a debian based distro like Kali Linux - I personally started with tools like nikto, camhacker... and then moved to more complex frameworks like metasploit.

I once had to give a presentation about Metasploit, and whether it was ethically correct for the creator to make it free and open-source, available to everyone. And in researching this I realized that there were a lot of parallels between the arguments for or against hacking tools being readily available and the arguments for or against gun control. I'll just list a few quickly:

Metasploit Framework (mentioned earlier)

This phase is where the pen testers practically prove that there exist potential vulnerabilities in the target system. The pen testers do the hacking using an array of technical approaches and social engineering methods to exploit the vulnerabilities. The ethical hackers commonly use Metasploit framework to automatically execute exploitation against the target systems. Moreover, they may install malwares such as rootkit to persistently maintain their foothold and further compromise the target system.