Apparently it IS possible to make IC's at home, obviously nothing approaching 5nm transistor gates and therefore the equivalent of lego blocks to precision machined parts... but anyways:
This stuff is half way up my professional alley and when I read it I had to think about the posts on hackaday the last 2 years which kind of document this new homebrew scene made of madmen.
I mean, anything can look like a conspiracy to a layperson who pays zero attention to 60 years of incremental progress and focuses solely on the end result. It's the same reason why people think vaccines are evil, or that 5G towers cause COVID.
5G towers do cause covid. Without 5G my WiFi would be far too shitty to book a cinema seat and get nice and infected by Karen her unvaccinated crotch goblins.
I could probably build a computer from scratch, but it's not gonna be a modern one with impossibly small microchips and bajillions of transistors. It's gonna be a room-sized behemoth with only like 8bits of memory that takes 24 hours to compute 1+1.
If you only care about adding numbers, you can e.g. do that using water or marbles. You only need to build an XOR gate, an AND gate and an OR gate.
In case of water, the gate will have two inputs as water streams. They should be aligned so that when the streams hit each other, the water will flow into a cup in the center of the apparatus. When the streams don't hit each other, the water passes the first cup and flows into another cup on the bottom. Carrying the water out at the bottom is the XOR gate, carrying the water out at the center is the AND gate and both cups together are the OR gate.
Then it's just about setting up the circuit and that would be a full adder without electronics.
I think TSMC's, a contract maker, market share is even 104.7%, not just around 61%. There are literally no other companies producing chips. Don't be fooled by sources telling you about a Korean company Samsung or made up words like Intel or Nvidia.