Answer:
You can start the project manager via the program RX‑TIMBER or via PRM64.exe.
Given a standard installation, the exe for RFEM is available at:
C:\Program Files\Dlubal\RFEM 5.xx
and for RSTAB at:
C:\Program Files\Dlubal\RSTAB 8.xx
The RX‑TIMBER program is always started via the project manager.
