ribbon cables can fail due to longterm overheating of device - especially after thermal paste expires and fan bearings become insufficient or otherwise burdened
Sounds like a ribbon cable needs to be reseated connecting board to the keyboard/trackpad
will require proper tools and a teardown video, but is resolvable - it's been a while since I've opened a surface so I'd need to know the exact year/model to further comment.
no idea why it happened right after the reinstall, that seems like a red herring to me because they were working at one point after the reinstall - for them to suddenly stop and persist beyond a power cycle signals hardware to me.
Even if our elections were "democratic" (they aren't), there is absolutely no chance of voting this shit away before it is foisted onto the population.
I wouldn't put it past Trump to have signed off on martyring a low-importance asset in a moment of precarious media-climate.