I'm actually dual-booting ublue (rebased to it from silverblue) and windows right now. When setting it up I didn't even know about any potential troubles lol. On my laptop they live on two separate drives with two separate EFI partitions, grub detected the windows bootloader and it's been working perfectly (no broken bootloaders, no windows getting before grub in boot order) for about a year now
Been using Silverblue for about a year now with no issues, recently rebased to ublue Nvidia for extra stability and some other perks. For my use case (web browsing, document viewing and editing, coding) it's been perfect. My coding environment lives in an arch linux container, all my other apps are flathub flatpaks