The issue that has occurred a few times is that some windows updates will decide that they 'own' the disk it's installed on or knows better than whoever is running the system, and overwrite any other boot manager with window's own and you may need to break out a live boot to recover it. Using a single isolated disc at OS install time (if you can have multiple physical drives) and using a motherboard boot selection hotkey means that risk likely goes away.

I use BIOS boot selection to dual-boot. MS has broken it twice. I turned off SecureBoot now and just don't run games that require it.

Apparently you can get a mobo with switchable BIOS config (or was it just a switchable SSD?) so the OS didn't even know that there's a second OS around. If there's no connection of the other OS then MS can't break it [as easily]!

IMO it must be malicious, because otherwise it would be caught with remedial testing. I can't believe MS don't include dual boot setups in their testing.

Many newer computers now have a rudimentary bootloader integrated in the EFI. Some are actually quite nice, allowing you to browse partitions to choose which image to boot. HPs have this. You just hit a key during uefi “post” and voilà.

The functionality is present on my new Lenovo laptop, various generations of HP elite/pro books/desks, old asus mobo and newer cheap gigabyte mobo, 7th gen intel nuc.