That isn't the point of Trump signing it. One of the finer points of that Act is that the President can not transfer power if the country is at Defcon 2 or 1. If you recall, the Capitol riots put the country into a COGCON 2. Now COGCON isn't the same as Defcon, but I'll bet that rule still applies since COG (continuity of Gov't) is what the restriction of transferring power is really all about. So it boils down to whether Trump is still President? "IF" the Insurrection Act was signed prior to the 20th and "IF" it is still in effect and "IF" COGCON 2 has the same rule about the transferring of Presidential powers as the Defcon 2 rule, then yes, Trump is still the POTUS. Chew on that one.