No. It means system gets mounted by flashing kernel or enc disabler and magisk won't flash with a mounted system.
thats about this,phone dont start,loading in download mode
rocess from bone stock
1. Flash TWRP.tar in Odin
2. Reboot directly into TWRP
3. Format data, reboot recovery
4. Flash kernel
5. Flash encryption disabler if desired.
6. Unmount system, Flash Magisk 19.4 (not 20.*)
7. Reboot system