Yes, the bath can be put on top of the panels. With the installation steps followed, you create a permanent connection to the plywood, which is the load bearing component in the structure.
In case you have further questions towards the installation steps, please consider the information of this digital brochure: KAQ_KFS_TileUnderlay_Brochure_EN_LR.pdf (aquapanel.com)
Page n°4: indicates the minimum subfloor thickness, that is relative to the distance of the wooden joists
Page n° 5: the construction scheme for AQUAPANEL Cement Board Floor Tile Underlay
Page n° 7: In case you require, a step by step process for the installation
Also in this landing page, you will be able to find a video of the installation process: KNAUF AQUAPANEL – AQUAPANEL® Cement Board Floor Tile Underlay