As I understand it, this is specifically not allowed by the DMA, since it would be considered an unfair advantage to Safari, if that browser/engine was the only one allowed to run PWAs.
https://eur-lex.europa.eu/legal-content/EN/TXT/?toc=OJ%3AL%3...
If Apple demonstrates that the entry barrier is sufficiently low by cooperating with other vendors, how one could possibly build a legal case under DMA against them? On the contrary, by disabling PWA in Safari Apple acts as a gate keeper complicating access to the platform for business users. THIS is what DMA forbids.
Also it has to be taken into account that the less PWA engines exist the lower is actually the entry barrier. We only need 2-3 competing solutions max to support innovation without harming PWA developers.