Upstream, dosfstools respects SOURCE_DATE_EPOCH since this commit:
8da7bc9331
This means tools like mkfs.vfat will create deterministic outputs when SOURCE_DATE_EPOCH is set.
A backport in nixpkgs is warranted since this was already merged in 2021 and no release of dosfstools has been made since then.
Co-authored-by: Paul Meyer <49727155+katexochen@users.noreply.github.com>