The Avengers were already disassembled in Infinity War, with the core group still split after the events of Civil War.
Avengers: Disassembled has also been guessed and that would be ominous, but Assemble would actually make more sense given the presumed plot.
We know that while Infinity War is the beginning of the end, Avengers 4 is the end of the end, the culmination of Phase Three and the MCU era that began with Iron Man.
Maybe that’s not it (especially since that’s what 2012’s The Avengers was titled in the UK), but I suspect that the answer is probably right in front of us and we’re just missing it.