It works on flashtool with Xperia 5 II on latest flashtool.
When you download the firmware from xperiafirm you need to create a bundle in flashtool with all the firmware files (make sure you delete the fwinfo.xml file before creating the ftf)
Then you need to rename the script file located in [C:\Users\Your User\.flashTool\devices\XQ-AS] to 58.0.fsc if that is your model and firmware number.
Then flash and exlude the TA files.