Official comment
@Donato > I'll give you the same answer I gave previously... rekordbox 5 was never going to have any updates after the release of rekordbox 6, but then the decision was made to provide one final update for Big Sur compatibility for those users who opted not to upgrade to 6.
This compatibility update is still on its way, but we are not providing a timeline. I'm sorry if you are in a situation where rekordbox 5 does not work for you, however there are two options:
1) Roll back your OS to a version that is supported.
2) Upgrade to rekordbox 6.
There are no plans to include support for the FLX6 in rekordbox 5.