Preventing users access to new technologies, forcing developers to remove features from their apps, preventing users from installing software that has certain functionality or content that Apple doesn't like (for example, even though marijuana is legal in many states, Apple has decided that all apps related to "vaping" are bad and not allowed on the app store) – these negatively impact users.It's hard to make a case that Apple is being anti-competitive in the US when US antitrust looks at whether harm has been done to consumers, and a strong argument can (and has been) made that the App Store is to the consumer's benefit.
I also look at the state of politics in the US and as a general rule of thumb, I find that the more divided the government is, the less likely it is for any major legislation passes which specifically targets Apple. Republicans are mainly going after social media companies for what they perceive to be a censorship bias, while the arguments made by democrats are pretty weak in my book.
In the US at least, I will say that Apple is in a far less precarious position than the press makes it out to be. Lawmakers on both sides are just not going to be able to agree on how best to craft legislation to rein Apple in, when they can't even agree on just what sort of harm Apple poses, and to whom exactly.
It may get more traction in the EU which looks at harm to businesses, but I expect Apple to still have a card or two up their sleeve. We have just have to wait and see, I suppose.
A couple of years ago Apple revoked the enterprise certificate for Facebook because they found out Facebook was using the certificate to allow users to install a certain type of app outside of the App Store. This instantly prevented that app from running on tens of thousands of user's devices (which also prevented those users from getting paid by Facebook which was a primary feature of the app. It was essentially the equivalent of Progressive's Snapshot monitoring device for cars but for smartphone users.). It also disabled Facebook's internal applications for ordering food from their campus restaurants amongst other things causing significant damage to Facebook and their employees for several days.
Since Apple also has insisted on controlling all means of installing software on iOS devices, while the app store itself can be viewed as beneficial, there is harm being done to consumers by demanding absolute control of the means of installing software.