I have read similar questions on various websites but haven't solved my issue. Thanks in advance for your help.
I installed Ubuntu on a Dell server with Windows 10 pre-installed as dual boot.
During booting, Windows 10 is not in the GRUB boot menu.
However, I can still boot into Windows by pressing F12 during booting to get into BIOS? then choosing Windows BootMgr.
$ sudo ls /boot/efi/EFI
BOOT ubuntu
$ sudo efibootmgr -v
BootCurrent: 0001
Timeout: 1 seconds
BootOrder: 0001,0000,0008,0009,000A,000C,000D,000E,000F
Boot0000* Windows Boot Manager HD(1,GPT,1a291e8a-bf72-4171-adb6-6244b30625ee,0x800,0x145000)/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.}...e................
Boot0001* ubuntu HD(5,GPT,015d35bf-e5ff-4267-8fe3-d0b70583083f,0x7286c800,0x1ad000)/File(\EFI\ubuntu\shimx64.efi)
Boot0008* Onboard NIC (IPV4) PciRoot(0x0)/Pci(0x1c,0x3)/Pci(0x0,0x0)/MAC(e4b97af857c8,0)/IPv4(0.0.0.00.0.0.0,0,0)..BO
Boot0009* Onboard NIC (IPV6) PciRoot(0x0)/Pci(0x1c,0x3)/Pci(0x0,0x0)/MAC(e4b97af857c8,0)/IPv6([::]:<->[::]:,0,0)..BO
Boot000A* Diskette Drive BBS(Floppy,,0x0)..GO..NO[.......+.D.i.s.k.e.t.t.e. .D.r.i.v.e.........................rN.D+..,.\...........BO
Boot000C* Hard Drive BBS(CDROM,,0x0)..GO..NOS.......+.H.a.r.d. .D.r.i.v.e.........................rN.D+..,.\...........BO
Boot000D* USB Storage Device BBS(PCMCIA,,0x0)..GO..NOc.......+.U.S.B. .S.t.o.r.a.g.e. .D.e.v.i.c.e.........................rN.D+..,.\...........BO
Boot000E* CD/DVD/CD-RW Drive BBS(USB,,0x0)..GO..NO........o.C.D./.D.V.D./.C.D.-.R.W. .D.r.i.v.e....................A...........................>..Gd-.;.A..MQ..L.Z.K.J.P.E.3.1.J.2.5. .7. . . . . . . . ........BO
Boot000F* NetWork BBS(Network,,0x0)..GO..NO........g.N.e.t.W.o.r.k.........................rN.D+..,.\...........8..Gd-.;.A..MQ..L.K.i.l.l.e.r. .E.2.4.0.0. .B.o.o.t........BO
Under Linux, failed to find bootmgfw.efi
with sudo find . -name "bootmgfw.efi"