Git 2.38.0 is the version where git archive uses an internal gzip implementation instead of calling the actual external gzip. This internal implementation has two improvements for this purpose: First, it doesn't store the timestamp. You could also get that with gzip -n. (But the old git archive didn't do that, so you have to run the gzip as a separate step after git archive.) Second, it stores the platform identification bits as "UNIX" on all platforms, so the output is identical on all platforms. There is no gzip command-line option for that, unfortunately.
Ah right. My suggestion would have been to use a small Perl or Python script or something, assuming there would be a zip library that would let you set the proper flags.
