In Monterey 12.3, I am no longer able to export a HAR file consistently. If I open the developer tools, and capture traffic, clicking on the "Export" button, or context-clicking and choosing "Export HAR" does nothing. I'm never prompted to save the file.
At times, it does allow me to export a HAR file, but only about 1 in 10-20 page loads. It doesn't seem to be specific to a site, or specific to anything environmental...it just seems to not prompt.
One other thing I've noted, when attempting to export the HAR file, Safari itself seems to freeze briefly (the spinning "beachball") - but after it starts responding again, there still is no prompt for saving the HAR file.