They just need to start giving a shit. Care about bugs for once. The whole software org needs to take the time to go through their (clearly) enormous backlog of bugs, and shore up what they have.
The problem isn’t the architecture or vision or rethinking their stack, it’s that what they have is barely holding together under its own weight. They need to do the unsexy work of going through and shoring it up.
As for Siri, just give the job to OpenAI. Let them write the new thing, they’ll probably be done in a month.