Meta is planning to let people in the EU directly download apps through Facebook ads. They plan to take advantage of new regulation in the EU called the Digital Markets Act (DMA), which will force Apple and Google to open up their mobile platforms to alternative methods of downloading apps.
Are you really confused though? Clearly OP just meant Android.
On Android you already have the ability to side load apps. I haven’t read the specifics of the EU rule but I’d imagine it either sets side loading in stone or has rules to make the side loading process easier