We'll wait and see about that.
Cause thankfully the legislation includes very explicit anti-circumvention clauses. 👏
"The gatekeeper shall not engage in any behaviour that undermines effective compliance with the obligations of Articles 5, 6 and 7 regardless of whether that behaviour is of a contractual, commercial or technical nature, or of any other nature, or consists in the use of behavioural techniques or interface design."
"The gatekeeper shall not degrade the conditions or quality of any of the core platform services provided to business users or end users who avail themselves of the rights or choices laid down in Articles 5, 6 and 7, or make the exercise of those rights or choices unduly difficult, including by offering choices to the end-user in a non-neutral manner, or by subverting end users’ or business users' autonomy, decision-making, or free choice via the structure, design, function or manner of operation of a user interface or a part thereof."
"The gatekeeper shall technically enable end users who decide to set that downloaded software application or software application store as their default to carry out that change easily."
Admittedly, this is the stuff that makes for disputes.
Will Apple try to make sideloading as difficult and convoluted as possible? Maybe.
But given that sideloading and third-party app store exist today and given how they work, I don't think the EU-mandated one can or will be more convoluted.
Personally I think this is going to be interesting. Especially once it has had time to evolve.
The default ability is the one I am watching most.