So why did that suddenly start happening in ~2024 when Toyota had decades when they could apparently clean out machined parts ?
It was a completely new twin turbo V6 design, not related to the older ones. One of their first to be fully computer optimized in design to use the least material and be most efficient. As a gross oversimplification, it turns out that some of the holes in the casting were blind or at weird angles and as such swarf got stuck in there and was not being properly washed out as part of the normal manufacturing procedure. The V35A motor has been redesigned for model year 2027 to hopefully fully fix the problem such that additional attention and hand cleaning is not required for those engines.
https://www.youtube.com/watch?v=6QKr9qIgIEM
If you watch the above video, you’ll see that the tolerances are so fine that even a tiny bit of swarf that got missed will kill the motor, usually by spinning the main bearings.
There are other opinions out there, but the consensus is that in this case, it’s likely the answer.