Why can't I create a new signal activity file (.saf) using the file browser to specify the Output file name for Write out signal activities to report file?

Due to a problem in the Intel® Quartus® Prime Software v18.0 and earlier, you can't create a new signal activity file (.saf) using the file browser to specify the Output file name for Write out signal activities to report file in the Power Analyzer Settings.  Even if you input a file name into File name field, the Open button is still grayed out and doesn't work.  You can only choose an existing .saf using the file browser in the operation.

1. Create a file with .saf extension in the destination to save in advance.  The .saf doesn't need to have any specific content.
2. Open the file browser of the Output file name for Write out signal activities to report file in the Power Analyzer Settings.
3. Choose the .saf created in step 1 and click Open.
4. The .saf is overwritten with signal activities after executing the Power Analyzer.