Enabling Re-Size bar in my BIOS also enables 4G automatically. CSM goes from the default of Enabled to Disabled.
This turns all of my drives to non bootable.
If I then set CSM Enabled again my system wont boot so have to do a CMOS clear, set back to defaults etc.
Having to do a Windows re-install for UEFI mode that can't be right can it? Will Re-Size bar ever work with CSM mode enabled?
Can't you "just" convert your HD's as needed to GPT from MBR, guessing that is needed..? It is going back some time since I did that but using diskmgmt / EaseUS Partition Master helped..?
https://www.wintips.org/how-to-change-legacy-to-uefi-without-reinstall-windows-10/
backup with Reflect or something first and wait a bit for someone else to offer advice along these lines, just to make sure.