From an anonymous user on secure boot

[Drummer]

App told me secure boot was not enabled.
(It was) App didn't recognize my actual grub
configuration. (Just wanted to set Windows as default. I
already have A Linux Mint option set) I didn't want
to break my actual configuration.

[Drummer]

Grub2Win reads this Windows system registry key to get the secure boot status.

A value of 0 means disabled 1 is enabled.

"HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Secureboot\State\UEFISecureBootEnabled"

So this is what Windows believes your secure boot status is.
You may want to check the key yourself to see if your machine is correct.

You can add Mint to your Grub2Win boot menu without harm.

Just run Grub2Win and click the yellow "Manage Boot Menu" button.

Then add a Mint entry and select the correct Linux partition.