This is likely because meson based build does not check for zlib, nor consequently set FREECIV_HAVE_LIBZ. At least there's such a bug, and it would explain why client doesn't recognize gzipped scenario files.
Need to rework the patch to consider emscripten build.
main/S3_2 patch completely rewritten to match zlib handling changes previously made on those branches, for emscripten support.
S3_1 patch updated to avoid duplicate libz detection (use this same detection also for libfreeciv linking)
Windows gtk3.22-client did not list any scenarios when I tested #47826.
I suspect this is general (not specific to that patch, or even Windows) problem with installed scenarios that the installation process has compressed. The client looks for files with suffix ".sav", not ".sav.gz"