Very slow render on 2 CPU machine HP Z840 Workstation

The biggest problem with that workstation is simple: Its installed GPU is outdated. That Quadro M4000 is now almost a whopping 10 years old (and based on an architecture that's almost 11 years old) at this point, and it has been depreciated for CUDA support in newer drivers. Specifically, although CUDA is still supported in newer drivers for that GPU Nvidia is now concentrating on the RTX GPUs (initially sold as Quadro RTX, then just plain RTX and now RTX PRO) from this point going forward. That means the Quadro RTX (and the related T-series) GPUs are now the oldest generation to continue receiving CUDA updates. And all pre-RTX GPUs will soon fall into legacy driver support status.

What happened in your workstation was that renders in both After Effects and Premiere Pro called for hardware acceleration of certain features that older GPUs did not support at all, which resulted in the rendering of those features falling back onto the CPU in software-only mode or not rendered at all, which in turn negatively affected the overall performance score of that workstation. Worse, most of the effects that got sent to the CPU instead of the GPU are only single-threaded when software-rendered. In other words, both After Effects and Premiere Pro expected a CUDA Compute Capability version of 7.5 or higher, but that M4000's CUDA Compute Capability version was only 5.2 (and the compute capability version is completely separate from the CUDA driver version number). And you cannot change that at all in software; the version is permanently baked into the GPU hardware.

As a result, you really need a newer-generation GPU just to keep that Methuselah of a workstation competitive in performance, although that 11-year-old CPU platform will not come anywhere close to matching a recent-generation CPU platform in overall performance.