I find it ironic when it comes to Nvidia they have close to a monopoly in GPU sector, and since they were the leading market share over like 65% if not more CMA blocked the arm deal. Which they should. If Nividia had Radeon's marketshare the deal would have gone through.
Eh, TBF to Nvidia, they do have a near monopoly on discrete GPUs, but that's because they've managed to navigate that market better than competitors. They didn't ruin their own chances like 3Dfx or Cyrix; AMD's been trying to beat them for years but still have things to do in order to beat years of mindshare Nvidia have gained in the GPU market. And if you're also factoring in iGPUs, Intel leads Nvidia by a landslide in market share.
I don't know if Nvidia buying ARM would have been approved if they had Radeon's market share, because ARM is SO ubiquitous with mobile CPUs. Nvidia buying them would be like when Intel were the sole holders of the x86 license, which they were forced to eventually give licenses to companies like AMD. If Nvidia got ARM, they'd of been forced to do the same, most likely. That would've been a massive concession and one Nvidia probably would've been really upset about.
The whole stuff with monopolies is weird because AFAIK, regulators don't really care if a company has a monopoly in a space. It's how they got the monopoly that matters. Like, Sony have a monopoly in console gaming (they have more than 50% of the home console gaming market), but they earned that market share by having a product appealing to the majority of customers versus their direct competitors. They were never found guilty of price dumping, price fixing, predatory pricing etc. or illegal exclusionary contracts, stuff like that.
So I think while that may by some definition be a monopoly, it's a legal monopoly because it's just the customer market rewarding who they feel earned the most of their money, and that's Sony/PlayStation. Steam would fall under a similar definition: they own almost all of the PC gaming market in terms of storefronts, but that's mainly because they catered to a market when it was still young, grew it, and have built up loyalty through having what many consider the best storefront on that platform for gaming.
Microsoft has a history of buying their way to majority market share in some markets, or buying their way to huge revenue increases, by just purchasing smaller companies. In some ways that's what it looks like they're doing again, this time in gaming having bought Zenimax and now trying to buy ABK, and that method is probably more what would have regulators concerned rather than a scenario where Microsoft has majority market share or revenue over a competitor. If they earned that by selling a product that most customers deemed superior and therefore purchased over rivals, that wouldn't cause
any issues. That's just capitalism at work.
Buying large publishers and folding their revenue streams into your own gaming division's though, in ways that could then be immediately leveraged for big market plays, deals etc. (but not necessarily "earned" by gamers buying more of your product leading to the revenue increases in the first place)? That could potentially be an issue.