We have them. The RAD750 for example (on the JWST and Curiosity rovers https://www.theregister.com/2012/08/08/mars_probe_cpu/ ) costs about $350k, has the architecture of a PowerPC 750 (the blue and white PowerMac G3), and runs at up to 200 MHz.

We have robust, space-worthy electronics. They're discussed in the article. You just can't get SOTA performance from them, because of fundamental physics-driven compromises.

We have been relying on natural magnetic fields for over a billion years, so we can probably continue doing so for a while.