update-grub cannot find Windows 10

I installed Devuan using the default installation procedure on sda. I've had serious problems with Windows 10 walking on my linux installations, especially during Windows updates, so I physically unplugged the linux hard drive and installed Windows 10 on the remaining hard drive, sdb. I figured I would install Windows, run update-grub, it would detect the Windows installation, and everything would be fine.

WRONG!

In the BIOS, I can choose to use the boot loader on either disk, and both work. It's just that grub can't detect Windows. I'd prefer to not change the BIOS settings each time. I've even gone so far as to setup the EFI partition in /etc/fstab. No joy.

I've done some research and I now believe what is wrong is Windows 10 is installed as UEFI and Devuan Linux is installed as legacy. (I hope I used the correct terms here.)

Here's the result of some possibly relevant terminal commands:

update-grub
Code:root@XXXXX:~# update-grub
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-4.9.0-12-amd64
Found initrd image: /boot/initrd.img-4.9.0-12-amd64
Found linux image: /boot/vmlinuz-4.9.0-11-amd64
Found initrd image: /boot/initrd.img-4.9.0-11-amd64
Found linux image: /boot/vmlinuz-4.9.0-6-amd64
Found initrd image: /boot/initrd.img-4.9.0-6-amd64
donefdisk -l
Code:root@XXXXX:~# fdisk -l
Disk /dev/sda: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: dos
Disk identifier: 0x(hexadecimal)

Device Boot Start End Sectors Size Id Type
/dev/sda1 * 2048 2000895 1998848 976M 83 Linux
/dev/sda2 2000896 66000895 64000000 30.5G 82 Linux swap / Solaris
/dev/sda3 66000896 1066000383 999999488 476.9G 83 Linux
/dev/sda4 1066000384 1953523711 887523328 423.2G b W95 FAT32

Disk /dev/sdb: 465.8 GiB, 500107862016 bytes, 976773168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: [hexadecimal and some dashes here]

Device Start End Sectors Size Type
/dev/sdb1 2048 1085439 1083392 529M Windows recovery environment
/dev/sdb2 1085440 1288191 202752 99M EFI System
/dev/sdb3 1288192 1320959 32768 16M Microsoft reserved
/dev/sdb4 1320960 976773119 975452160 465.1G Microsoft basic datalsblk
Code:root@XXXXX:~# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 931.5G 0 disk
a"a"sda1 8:1 0 976M 0 part /boot
a"a"sda2 8:2 0 30.5G 0 part [SWAP]
a"a"sda3 8:3 0 476.9G 0 part /
a""a"sda4 8:4 0 423.2G 0 part /SHARED/local
sdb 8:16 0 465.8G 0 disk
a"a"sdb1 8:17 0 529M 0 part
a"a"sdb2 8:18 0 99M 0 part /EFI
a"a"sdb3 8:19 0 16M 0 part
a""a"sdb4 8:20 0 465.1G 0 part
sr0 11:0 1 1024M 0 romI suspect I'm going to have to zero both drives and reinstall Windows first so that Devuan can see the EFI partition and load in UEFI mode, right? Or is there some way to extricate myself from this morass without reinstalling?

This computer is a sandbox more or less. I need to figure out all this UEFI...stuff...before I replace the hard disks on my main desktop with SSDs. Do I need to tell Devuan to install as UEFI or will it figure this out from the existence of the EFI partition?

How do I keep future Windows updates from walking on my Devuan boot? I only use Windows for games that do not have a Linux version, so security isn't that much of an issue, but I'm pretty sure that on occasion, Windows doesn't ask if I want updates, it just steamrollers ahead with them.

Thanks in advance!