I received the following warning when installing KDE 21.1.4 minimal with manual partitioning. I had selected to mount my laptop’s existing 260 MiB EFI system partition at /boot/efi.
No EFI system partition configured
An EFI system partition is necessary to start Manjaro.
To configure an EFI system partition, go back and select or create a suitable filesystem. The filesystem must be mounted on /boot/efi. The filesystem must have type FAT32. The filesystem must be at least 314572800 MiB in size. The filesystem must have flag boot set.
You can continue without setting up an EFI system partition but your system may fail to start.
The only one of these “requirements” that I hadn’t met was the 314572800 MiB in size. I chose to continue, and the installation succeeded.
The problem is that you are stating a person’s EFI system partition must be 300 TiB in size. I’m sure you meant to make it 300 MiB, but that will still trigger this warning for many people because Windows computers come pre-installed with an ESP of 100-260 MiB.