I don't have the technical details but I know roughly which area of the system it targets. The exploit takes place after the boot process, I guess it's unpatchable because patching it would break compatibility with old software. I'm not going to give away too much detail because if I do I might not get private info in the future. I heard they were having trouble trying to monetize it in a way that couldn't be easily stolen by other people and since their Switch chips were selling well it wasn't a priority. They aren't going to just give it away because they're TX, I don't think they've gave stuff away for free once in their 20 year history.
As for the PSP being exploited. I don't think that has happened on the Xbox? It uses the same PSP as the PlayStation but the vulnerability what was documented needs UART or SPI to be enabled, which is enabled on PlayStation but only rare Xbox devkits have it enabled (the god boxes documented here
https://titleos.dev/xdk-buying-guide/ ).