Showing result on display and log file at the same time

If you use the "--logfile" option, the all result is output only to a file, but I need to have both a file and output to the screen in real time. Utilities like "tee" are not suitable, they display the result on the screen only after "iperf" has completely finished executing. What is the point of using this option? It doesn't work as it should ))) You can just redirect the output without using this option, it will be the same )) But output to the screen in real time and output to a log file at the same time are very necessary, but they don't work )