For UEFI installs, just don't assign the EFI /boot partition, then no bootloader gets installed.
If you boot in legacy BIOS mode, make sure to tick
don't install bootloader.
Default settings used in Dolphin was KaOS community chosen. Putting a panel vertical might be new to you, but try it a while if you are on a (most common now) widescreen, and you will find it is much more intuitive. If not to your liking, just drag the panel to where you then prefer. No need to keep all as Windows default, no harm in showing other workflows, some will hate, some will be surprised how much better it fits their workflow.