Your first example only works for goods that are completely optional, which is very rarely the case. For example, smartphones. Nobody technically needs one, but almost everyone in western countries has one. If every company that makes a smartphone increases their prices, people will still buy them because they basically need them. I believe this is the principle of inelastic demand (or low elasticity) -- car fuel is a more traditional example.

Your second example doesn't work when the cost of entry into the market is really high. This is very common in high tech. Take semiconductors for example. There's basically one big name in chip manufacturing (TSMC) and a few runner-ups (Samsung, Intel, etc.). The latest node is infamous for being very expensive and low capacity. Why aren't there new competitors constantly breaking in to the market?

UBI is a great idea and will help things, but it's not perfect so we shouldn't expect it to just completely fix capitalism. The best way to fix capitalism is to get governments (which are all in charge of capitalism) to fix it with regulations. UBI will be a major regulation/step in the right direction.

When there’s a dozen manufacturers, they won’t all do it. As I mentioned, this is price fixing and illegal in a lot of countries.

They can't coordinate together to fix prices, but there is nothing legally stopping them from watching each other's public behavior and adjusting their pricing to match.

All B has to do is not raise their prices as much as A.