

I imagine there is both scenarios happening.
Take for example, Apple. They have Mac /MacOS but for a long while ( I can’t confirm currently ) they were using Windows PCs to design their products–even though their CAD software they used had a Mac version.



While 2 drives is better, you can safely dual boot on one drive by making 2 EFI boot partitions. Install Linux on its own EFI and the probe foreign OS will find windows and add it as a chain loading entry. Set UEFI to boot from Linux partition. Windows will ignore the 2nd EFI and only mess with it’s own.
If windows promts to add a drive letter on first boot (to the new efi and Linux partitions) just decline and choose the option to ignore in the future.