My final folder for the customization is: /opt/bitnami/apps/joomla/htdocs/templates/g5_helium/custom/components/com_comprofiler/plugin/user/plug_cbactivity/templates/default/core/display
is that correct? from which level should i enter the path? starting with templates/g5_helium or starting wiht opt/bitnami?
No, that is not correct. You need to create your template folder in CB Activity template folder. Example as follows.
Default:
/components/com_comprofiler/plugin/user/plug_cbactivity/templates/default
Custom Template
/components/com_comprofiler/plugin/user/plug_cbactivity/templates/mytemplate
Custom Template Override
/components/com_comprofiler/plugin/user/plug_cbactivity/templates/mytemplate/core/display/article.php
Now select your template within CB Activity > Parameters > Global.