The Constitution states, "...shall be removed from office on impeachment for and conviction of treason, bribery, or other high crimes and misdemeanors." It is left to the house to define high crimes and what misdemeanors are. In theory the house could consider spitting on the sidewalk a misdemeanor. But whatever the charge, it will be some high-falutin sounding very official charge like violating the Constitution or something like that. How about issuing unconstitutional mandates?
I think you’re looking for a valid, reasonable cause or reason for impeachment of Biden from a Republican controlled house. Do you really expect that? What I’m predicting is the reason, the charge will be very formal and official, sounding very serious, but the real reason will be payback for impeaching Trump twice regardless of whatever the charge states.
It is entirely up to the House of Representatives to define and determine exactly what an impeachable offense is.