Conversation so far:
who left vampire weekend?
Rostam Batmanglij announced his departure from the band on Twitter.
why?
collaborate.
What did he want?
Batmanglij contributing to the record.
The album's working title was revealed to be Mitsubishi Macchiato.
What did he move on to?
Koenig revealed in an elaborate Instragram update that during 2016 he had spent countless hours researching and writing music in libraries with grad students.
When was it realesed?
Initially, this news was regarded a rumour, until the band's website revamp in 2018, in which a Sony Music copyright appeared on the site.
What did he  try to do next?
Additionally, he revealed that the album would feature a more 'spring-time' vibe and one of the songs would be entitled Flower Moon.

Question: What did they do?
Self-contained rewrite: What did Rostam Batmanglij do after revealing what Mitsubishi Macchiato would feature?