We have a machine at our house we use for banking that we want to be secure - we chose an iPad for this purpose. I am very worried about Apple being legally compelled to add the necessary code to iOS/iPadOS to allow people to download and install apps from the web like with Windows and macOS, which would be a requirement for 3rd party app stores. It means we will no longer have such a nice solution. Nothing will ever be as secure as the total program whitelisting iOS/iPadOS has now.
Apple does not have a monopoly. Monopolies require you to have all or nearly all of the market share for your product, and in the case of Apple, Android actually has way more users than they do. As far as I'm concerned, Apple doesn't have to allow third-party apps on their platform at all if they don't want to any more than I'm required to allow guests into my home. IIRC that was exactly the situation when the iPhone first came out - their apps and nothing else. I don't see any calls for my Mom's simple calculator to be required to write a solution to allow third-party firmware to be flashed onto the device on the basis that they have a "monopoly" on their calculator's firmware.
This is the most ridiculous thing I've ever seen, but with the situation progressing as it is in Europe, I think Apple is really going to lose this one. Outside of Apple fan sites, people seem to be overwhelmingly in favor of that outcome.