Once the States certified their election results and chose their Electors for the Electoral College on December 14, 2020 the election was over.
According to the US Constitution, Biden is the legitimate President elect of the US. However, that does not negate the fact that the State elections in at least ten States were conducted illegally according to their own State laws.
Article II, Section 1, Clause 2 of the US Constitution clearly states that the State legislatures determine the electors for the Electoral College. So the State legislatures could have just flipped a coin to determine their electors and it would have been constitutional. The vote of the Electoral College has nothing to do with the State elections and how they got there, as long as they were appointed by the State legislatures as required by the US Constitution.
We haven't even begun to see the fall-out of what those ten States did when they deliberately violated their own laws. Alaska was one of those ten States, and the State AG has until November 2, 2021 to prosecute the government officials responsible for violating Alaska's election laws. Impeachment proceedings have also been started against Alaska's Supreme Court Chief Justice for illegally interfering with Alaska's election laws. He chose to resign in June, but I'm hoping the State legislature impeaches him before then.
With regard to Trump passing anything, I'm afraid you need an education in basic civics: Congress enacts the laws, not Presidents. Congress raises or lowers taxes, not Presidents. Before you ignorantly claim the President must sign a bill before it becomes law, that is also false. All bills passed by Congress become law automatically after ten calendar days (excluding Sundays) while Congress is in session - regardless of whether the President signs the bill or not. Furthermore, that 2018 tax cut passed Congress with a veto-proof majority. So the only reason Trump would sign such a bill would be to include a Signing Statement and for no other reason. In your ignorance of basic civics you are blaming the wrong responsible party.