Comment 7 for bug 1845289

Yes, by using the F12 key, I can display the EFI start menu and start Windows with the "Windows Boot Manager" line.

This is a test machine that follows the development of "Ubuntu next". Initially installed with Ubuntu 17.10 beta, it has followed the updates of all Ubuntu development versions (18.04, 18.10, ...) until today. Now in 19.10, it will soon switch to Ubuntu Focal 20.04).

The Windows part has been re-installed from scratch with an Windows 10 18.03 USB flash drive installer and regularly updated. Now running W10-19.03.

After installing Windows, Grub was re-installed by starting the machine with Ubuntu-Live 18.04 and then entering the following commands:
$ sudo mount /dev/sda2 /mnt
$ for i in dev sys proc dev/pts; do sudo mount -o bind /$i /mnt/$i; done
$ sudo chroot /mnt
# apt purge grub-common grub-efi grub-efi-amd64 grub-efi-amd64-bin grub-efi-amd64-signed grub2-common
# apt install grub-common grub-efi grub-efi-amd64 grub-efi-amd64-bin grub-efi-amd64-signed grub2-common
# update-grub
(... reboot → Ubuntu ...)
$ sudo update-grub

Everything was working well until more or less half-time of 19.10 developpement.

Here my partitioning :

$ sudo parted /dev/sda print
Model: ATA M4-CT512M4SSD2 (scsi)
Disk /dev/sda: 512GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags:

Number Start End Size File system Name Flags
 1 1049kB 1075MB 1074MB fat32 esp boot, esp
 2 1075MB 207GB 206GB ext4 Ubuntu
 3 207GB 345GB 137GB ntfs data msftdata
 4 345GB 345GB 16.8MB Microsoft reserved partition msftres
 5 345GB 512GB 167GB ntfs Basic data partition msftdata
 6 512GB 512GB 520MB ntfs hidden, diag