No, you don't have to reinstall Windows 10 in UEFI mode.
No, you don't have to reinstall Windows 10 in UEFI mode.
You're considering a switch to a new motherboard and CPU while dealing with legacy Windows 10 setup. It's important to reinstall Windows in UEFI mode if you want a smoother experience, especially since your current system had issues when adding the NVMe SSD and booting into BIOS. The advice about legacy mode affecting recognition is valid—upgrading from Z170 and 6600k might have been tricky. Make sure your new hardware supports UEFI and that you follow the proper installation steps for a stable upgrade.
All available boards support legacy mode booting, so you should still be able to start from your older drive. The NVMe storage unit shouldn't interfere with the initial setup—verify the boot sequence. A fresh installation is recommended for new hardware, and using UEFI during setup would be ideal.
I used nearly everything with that NVMe SSD, but nothing worked properly. It seems like I chose a problematic motherboard before. In the past, it would fail to boot or switch between BIOS settings even after saving it to a profile. Even more bizarrely, it would sometimes boot using a backup BIOS unexpectedly.
Convert your 10 to GPT for UEFI BIOS. Ensure you back up your data before proceeding.
You should have understood the update. I won’t be asking why you’re stuck on 1511.