Hello,
In the latest available version of the 3DExperience on the Cloud (FD07), it is possible to use a CATIA V5 Launcher to start the desired version. One of you has already managed to get it to work.
https://help.3ds.com/2021x/english/dsdoc/cv5adminmap/cv5-c-useapplauncher.htm?contextscope=cloud
Thank you for your help.