This won’t apply to all of Apple’s apps, just apps that would compete against other apps that are available in the App Store. This could potentially cover apps like calendar apps or weather apps where there are plenty of third-party alternatives in the App Store. The idea, presumably, is to give third-party developers more of a chance to be discovered instead of users defaulting to what’s already available.
According to U.S. House Judiciary antitrust subcommittee chairman Rep. David Cicilline, “It would be equally easy to download the other five apps as the Apple one so they’re not using their market dominance to favor their own products and services.” This wouldn’t just affect Apple but will also apply to other tech companies such as Amazon who create and sell their own first-party branded products that compete with third-party products also sold on their platform.
Note that this antitrust bill is merely a proposal and hasn’t been passed into law yet, meaning there is a chance that it might not, although even then, we imagine that Apple would probably fight to appeal it.