My guess is that f2 is being copied to the clipboard as an embedded image which doesn't support transparency. By default the print command uses a heuristic to determine how to generate the content for vector formats like metafiles.
You can force the print command to produce "true vector" output by using the -vector option (R2021b or later). In earlier versions of MATLAB you can use the -painters option:
print(f1, '-dmeta', '-vector'); % 21b or later
print(f1, '-dmeta', '-painters'); % 21a or earlier
In R2020a or later you can use the copygraphics command instead of print, which has the added benefit of eliminating the extra whitespace that typically accompanies a plot:
copygraphics(f1, 'ContentType', 'vector')
