The DMA explicitly forbids that. There must be no cost, and no barriers to distributing apps to iOS users. Apple cannot, for example, force developers to sign up with Apple, pay additional fees, or use special certificates.

Honestly, I think the DMA is the most impressive, most comprehensive technology focused piece of legislation in my lifetime. They've clearly gone to great lengths to consider all the ways gatekeepers like Apple might intend to maliciously comply. Further, the EU operates under the principle of "spirit of the law," as opposed to the US, which operates under the principle of the "letter of the law." This means judges don't take kindly to companies attempting obvious circumvention of the intended principles of the legislation. Even if Apple were to find a loophole, they probably won't be allowed to exploit it.