As far as I know there is no official preliminary report on the crash published yet. The Namibian CAA is responsible for doing the investigation and publishing a report.
The Mozambique CAA did a press release on December 21. They did a couple of statements. One of them is that the captain had a clear intention to do the things he did (decend, keep the speed below max). The Mozambique CAA did not state 'the captain had a clear intention to crash the plane' nor they stated it was suicide.
The press reported about 'intention to crash the plane'
Nobody at this stage knows why the captain did the rapid decend.