What, exactly, do you think Biden could have personally one to prevent the Supreme Court from doing what they were stacked by Trump to specifically do?

The president can't overrule the Supreme Court. He can't appoint any new judges until there is a vacancy.

And the economic crisis isn't a uniquely American problem. It's also impacting Europe, Canada, and most other western nations. What can the president of the US do to directly and quickly "fix" something of that scale? Something that had been several decades in the making?