As a workaround you could use ExifTool to copy the "Film simulation" to the Keywords field. This is a little advanced since it requires a command line tool, but once you know ExifTool it's pretty quick.
If you had ExifTool installed, you could do something like this in a folder of files and it would put the Film simulation mode in the keywords that would be readable by Photo Mechanic
exiftool "-Subject<FilmMode" *.JPG
If you're NOT familiar with ExifTool, be very careful using it. It can overwrite metadata if you make mistakes. For example, the way it's written above assumes you don't have any existing keywords (e.g. an early workflow step) and it would wipe out any keywords you already had. EXIF tool is very powerful though and if you learn it, it can help you solve a lot of metadata problems.
-Mick