Sadly, they have parted ways at this point. Not only has Ladybird broken off into an independent project but it does not consider SerenityOS a target platform anymore.
Ladybird is slowly shedding a lot of the “home grown” Serenity layers and replacing them with more mainstream alternatives.
As I am primarily a Linux user, I am excited to see Ladybird become a real alternative on Linux. However, as a fan of SerenityOS as well, I am sad to see all the energy and innovation that was going into Ladybird get stripped out of SerenityOS.
It's not about whether or not Apple have the resources to make their own browser engine, it's about whether it makes sense from a business point of view to make their own browser engine. Currently it does, because Google pay them huge amounts of money to do so. But what business case would there be to pay that $20bn themselves if Google did not fund them? Would it be worth that just to avoid Chromium?