Version 6 is a complex "coming when it's ready". You can read the very high level tasks that need to be done before it's ready here.
The old bootstrap 3 version is no longer supported and issues/prs relating to this will be closed except for security vulerabilites etc. The code base for this is in the v4 branch.
Need help or want to discuss the upcoming v6? Join our discord.
Please also take a look at the discussions. There are several RFCs (Request For Comment) open and you can help shape the future of the picker by participating in these discussions.