try this approach
In assign activity rowindex = "3" as string and then pass into selector <sap id='usr/tblZ_CA_MATERIAL' tableCol='-1' tableRow='" + rowindex + "' />
Cheers
If you leave tableRow=‘-1’, SAP UI defaults to the first visible row.
When you try to concatenate " + rowindex + ", it might not be building a valid selector string (e.g. quotes inside quotes issue).
Replace the tableRow value with a variable placeholder.
In the properties panel, for Selector, put,
“‘(sap id=‘usr/tblZ_CA_MATERIAL’ tableCol=‘2’ tableRow=’” + rowIndex.ToString + "’ )**
Check if tableRow really changes when you click row 0, row 1, row 2, etc.
If it doesn’t change, then SAP is not exposing row index this way the selector will never work.
Cheers
You can try using the Click ToolBar Button activity, which is specifically designed for SAP integration. If the issue still persists, we can connect on a meeting or else please share a screenshot so I can assist you further.