The main difference is with Biden it actually happened. With Trump you're claiming it would happen.
The mainstream media en masse blatantly ignored the obvious and severe cognitive decline of the friggin POTUS, lapping up the blatant lies from the WH and asking their viewers/readers to ignore the evidence of their eyes and ears.
If Trump started to repeatedly attempt to shake hands with imaginary people, forget close aides names, get lost walking off stage, mumble incoherently etc. Fox News very well might provide slanted coverage like they always do, but they wouldn't ignore it as if it wasn't happening at all, or accuse democrats who bring it up as being purveyors of cheap fakes.
This scandal is so far beyond the both sides are biased argument.