How to protect your computer from data theft?

Question

Information Security

As I understand it, it is possible to infect even UEFI and BIOS, which means that any OS and antivirus will not help. Does this mean that the best option is to buy a new laptop, reflash UEFI / BIOS on it, install, for example, Ubuntu with full disk encryption and not connect to the network, and install programs through downloaded packages tested on another computer with an antivirus?
I apologize for the noob question, but I'm zero in IS and I only know how to run a scan on Kaspersky.
P.S. Or am I overthinking and malicious programs are not often written these days, but mostly social engineering is used?

Answer 1

You don't have to start with this. You need to start with the question "Why?" Why the hell to fence such a garden? It's complicated. It's long. It's #oops so uncomfortable. This adds a real danger to sifting all the data if the encryption key is lost (I'm not joking at all - I store the keys of the mail certificates of the office in three different places).
Therefore, always start with a violator model. That is, from the answer to the question "why do I need data protection? Who (what) am I afraid of, what kind of things do I have that can harm me?"
And only then to fence all these events, because it may turn out that half of them are not needed.

Answer 2

From the OS, take some Haiku, Phantom OS. :-) I don't know anything about their security and usability, but it's unlikely that hackers will target their bots on such operating systems.