PIO to PIO between two rp2350s should be able to transfer as many bits per clock as you can spare pins for.

They have a single cycle double multiply per core, and the interpolators give you a heap of ability

The PIO can be awkward, but you can run a bunch of them at once. Going from MCU to MCU you don't even need to involve the CPU cores, PIO to PIO Comms via pins

You are obviously not going to get big TOPS from it because a Trillion is a ridiculous amount anyway. But never underestimate the power of controlling the whole pipeline.

Ultimately none of the other things I'm doing with MCUs are practical, why would this to be any different.