I agree with @Hook. That screen in the first screenshot should be shown while you use fastboot to flash the boot.img.
adb, on the other hand, does its job only from recovery, not from that bootloader screen. That said, just flashing the Magisk-patched boot.img (which I understand is what you are trying to achieve) does not require any action to be performed from recovery. You should not go there at all for this.
The no-command-screen usually indicates that the recovery image fails to boot. It normally should not be shown at any step of a reflashing procedure, and probably indicates t