The key difference is the OEM license agreements. Google includes dubious requirements in their licensing terms, such as the anti-fragmentation clause. But Apple does not license their software to OEMs, and so cannot run afoul of antitrust IP licensing issues.

Many (or most?) bundled iOS apps can be removed https://support.apple.com/en-au/HT204221

They have a duopoly [1]. The linked article explains what a duopoly is, and cites relevant examples. I can tell you of another very relevant US-centric example but its not in business: Republican and democrat.

The impact a duopoly has on a market is vastly different from a monopoly. One problem could be price fixing; but that could happen with more than 2 companies as well. Then we speak of a cartel.

The problem with a monopoly isn't per se that it exists; it becomes anti competitive business practices when the monopoly is abused to exercise control over other markets. I'd like to compare it with a benign tumor which ends up spreading.

[1] https://en.wikipedia.org/wiki/Duopoly

There is one difference: that’d be a Duopoly, not a Monopoly.

There is a huge practical difference and that is where their revenue comes from.