GRUB2 not chainloading Windows 10

[Steve Jensen]

Trying to dual-boot a Dell laptop. I have GRUB2 installed which boots
Linux fine. However, when I try to boot Windows ("Windows Boot Manager"
menu item in the GRUB2 menu) then the screen just goes black and no
activity occurs.
However, if I boot into UEFI/"BIOS" on poweron and select "Windows Boot
Loader" from the boot menu in there Windows boots fine.

I have the following setup:

- Dell XPS 13 (7390)
- Linux 5.4.6-arch1-1 #1 SMP PREEMPT Sat, 21 Dec 2019 16:34:41 +0000
x86_64 GNU/Linux
- os-prober 1.77-1
- grub 2:2.04-3

-Secure boot disabled
-UEFI ONLY boot setting (Legacy/BIOS booting disabled)
-Arch Linux installed in addition to Windows 10


The disk (only 1) looks like this:

Device             Start        End    Sectors   Size Type
/dev/nvme0n1p1      2048    1085439    1083392   529M Windows recovery
environment
/dev/nvme0n1p2   1085440    1290239     204800   100M EFI System
/dev/nvme0n1p3   1290240    1323007      32768    16M Microsoft reserved
/dev/nvme0n1p4   1323008  308760575  307437568 146.6G Microsoft basic data
/dev/nvme0n1p5 308760576  728190975  419430400   200G Linux filesystem
/dev/nvme0n1p6 728190976 2000409230 1272218255 606.7G Linux filesystem

GRUB2 was installed using standard

grub-install --target=x86_64-efi --efi-directory=esp --bootloader-id=GRUB

and os-prober found Windows all-right ("Windows Boot Manager" shows up
in GRUB2 menu.)

grub.cfg was generated with

grub-mkconfig -o /boot/grub/grub.cfg

and the relevant grub.cfg section looks as follows:

### BEGIN /etc/grub.d/30_os-prober ###
menuentry 'Windows Boot Manager (on /dev/nvme0n1p2)' --class windows
--class os $menuentry_id_option 'osprober-efi-6261-199D' {
insmod part_gpt
insmod fat
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root  6261-199D
else
search --no-floppy --fs-uuid --set=root 6261-199D
fi
chainloader /efi/Microsoft/Boot/bootmgfw.efi
}
### END /etc/grub.d/30_os-prober ###

grub.cfg was not manually modified.

"efibootmgr -v" shows the following output:

BootCurrent: 0004
Timeout: 0 seconds
BootOrder: 0004,0003,0000
Boot0000* UEFI KXG60ZNV1T02 NVMe TOSHIBA 1024GB 99GA22PBK3QL 1
PciRoot(0x0)/Pci(0x1d,0x4)/Pci(0x0,0x0)/NVMe(0x1,8C-E3-8E-03-00-20-84-29)/HD(2,GPT,950216ab-2bfb-4159-ad13-051bfb4c2311,0x109000,0x32000)/File(\EFI\Boot\BootX64.efi)N.....YM....R,Y.
Boot0003* Windows Boot Manager
HD(2,GPT,950216ab-2bfb-4159-ad13-051bfb4c2311,0x109000,0x32000)/File(\EFI\Microsoft\Boot\bootmgfw.efi)WINDOWS.........x...B.C.D.O.B.J.E.C.T.=.{.9.d.e.a.8.6.2.c.-.5.c.d.d.-.4.e.7.0.-.a.c.c.1.-.f.3.2.b.3.4.4.d.4.7.9.5.}...a................
Boot0004* GRUB
HD(2,GPT,950216ab-2bfb-4159-ad13-051bfb4c2311,0x109000,0x32000)/File(\EFI\GRUB\grubx64.efi)

I turned on debug=all in GRUB2 before trying "Windows Boot Manager"
entry and the output ends with the following (and it just sits there):

commands/verifiers.c:88: file: /efi/Microsoft/Boot/bootmgfw.efi type: 29
disk/efi/efidisk.c:593: reading 0x40 sectors at the sector 0x10b180 from hd0
kern/disk.c:196: Opening "hd0,gpt2’,,,
disk/efi/efidisk.c:482: opening hd0
disk/efi/efidisk.c:511;: m = Ox53d1f058, last block = 773bd2af, block
size = 200, io align = 8
disk/efi/efidisk.c:531: opening hd0 suceeded
partmap/gpt.c:90: Read a valid GPT header
partmap/gpt.c:112: GPT entry 0: start=2048, length=1083392
partmap/gpt.c:112: GPT entry 1: start=1085440, length=204800

Any idea why GRUB2 seems to be unable to chainload Windows Boot Manager?

Thanks!