Assuming Biden wins, attempting to prosecute Trump for whatever crimes committed prior Biden's inauguration will be perceived by his base a witch hunt. Considering his base's sheer fanaticism and numbers, combined with his cult of personality attempting to prosecute Trump will likely mobilize Republicans politically for the midterms and 2024, and possibly cause violent retaliation by the violent fringes.
Going after Trump would be a massive tactical and even greater strategic error. The best thing this administration can do for the next 4 years is to COMPLETELY IGNORE Trump. Assuming they can take the Senate in the Midterms and retain the House, they need to pick their fucking battles and focus on fixing the judiciary and winning in 2024, after that we can discuss going after Trump (if he's still alive) and his entire family.
Trying to do anything before that would be phenomenally counter productive.
Prosecuting the Trump's for anything they might do, if they do something shady (which they likely will) after January, that's a different conversation, but even then,
the DoJ should steer clear as much as possible from any direct involvement, using state prosecutors.