Okay, so I’ve tested with /boot/grub2/.grub2-blscfg-supported present and without:
Without
# grub2-mkconfig > grub-without-blscfg-file-present.cfg
# grep -E '(linux|initrd)16' grub-without-blscfg-file-present.cfg
linux16 /ostree/fedora-06001f603ad4e290e14fc32c517a16e13cef2ac16a38759e3434cef52c8dda8b/vmlinuz-5.15.7-200.fc35.x86_64 rd.luks.uuid=luks-8c20fbb2-ff0e-4192-a004-cccfa09f53c8 radeon.cik_support=0 amdgpu.cik_support=1 root=UUID=b3d495a2-c874-472a-85ff-32d4bec26119 rootflags=subvol=@ ostree=/ostree/boot.1/fedora/06001f603ad4e290e14fc32c517a16e13cef2ac16a38759e3434cef52c8dda8b/0
initrd16 /ostree/fedora-06001f603ad4e290e14fc32c517a16e13cef2ac16a38759e3434cef52c8dda8b/initramfs-5.15.7-200.fc35.x86_64.img
linux16 /ostree/fedora-0ce6da105f3a3d5c717d7b0b0d6864a61b215fa60c9b53c50f752d59f82d04af/vmlinuz-5.15.6-200.fc35.x86_64 rd.luks.uuid=luks-8c20fbb2-ff0e-4192-a004-cccfa09f53c8 radeon.cik_support=0 amdgpu.cik_support=1 root=UUID=b3d495a2-c874-472a-85ff-32d4bec26119 rootflags=subvol=@ ostree=/ostree/boot.1/fedora/0ce6da105f3a3d5c717d7b0b0d6864a61b215fa60c9b53c50f752d59f82d04af/0
initrd16 /ostree/fedora-0ce6da105f3a3d5c717d7b0b0d6864a61b215fa60c9b53c50f752d59f82d04af/initramfs-5.15.6-200.fc35.x86_64.img
With
# touch /boot/grub2/.grub2-blscfg-supported
# grub2-mkconfig > grub-with-blscfg-file-present.cfg
# grep -E '(linux|initrd)16' grub-with-blscfg-file-present.cfg
no output
So @guiltydoggy, it does seem like /boot/grub2/.grub2-blscfg-supported ought to be created by default on UEFI systems… 