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How do I add Windows to GRUB so that I can choose whether to boot into Ubuntu or Windows?

This and this and this did not work.

My output from boot-repair: http://paste.ubuntu.com/p/tGVBRn3YnK/

I have a machine with two 0.5TB SSDs and one 5TB hard drive. One SSD (sdb) has Ubuntu 18.04, the other SSD (sda) has Windows 10; sdc is the hard drive. From the grub menu, I was previously able to boot into either OS, but I recently did a re-install of Ubuntu and now I am unable to boot into Windows.

I sincerely appreciate the help.

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    Welcome to Ask Ubuntu. I know sudo update-grub is on your first link, but did you try it? (the links provide lots of answers, so you may not have tried all) – guiverc Aug 30 '18 at 1:21
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    It looks like you reinstalled Ubuntu in UEFI mode, while Windows is in legacy mode. Installing both in the same mode is the usual way, but some machines will boot either, with a preference for one if both are present on the same device. – ubfan1 Aug 30 '18 at 3:23
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    You can always boot from UEFI boot menu. But grub will only boot other installs in same boot mode. You do not have to reinstall, but add a tiny 1 or 2MB unformatted partition with bios_grub flag and using Boot-Repair in BIOS boot mode from Ubuntu live installer reinstall grub. You can the grub-pc version for BIOS boot. You only want grub on sdb, and a Windows boot loader on sda. Boot-Repair auto fix normally installs grub to all drives, but you want Windows boot loader on Windows drive. – oldfred Aug 30 '18 at 3:37
  • All very good options - thank you! Hours with IT and somehow reinstalling Windows was the answer. – Dan Y Sep 5 '18 at 1:02

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