I installed linuxdebian on a macbook and encountered some problems.

I installed linuxdebian on a macbook and encountered some problems-General Linux technology-Linux technology and application information. The following is a detailed description. I want to delete osx from macbook air and install debian. I downloaded debian_i1__cd_1.iso and installed it through usb cd-rom.
During installation, select no force efi; select guided to partition entire disk; select install grub in/dev/sda;
The problem after installation is:
1. it is slow to start. it keeps a dark screen after startup. After 1 minute, the grub menu appears. If no operation is performed, the system automatically enters the command line. If you press the option key and select the disk icon, the grub menu appears in about 10 seconds. If any option is selected when the grub menu appears, the startup fails.
2. the graphic interface cannot be started. I chose to install desktop entironment during installation, but only the command line is available after startup. type startx, some text will pop up and there will only be a command prompt at the top of the screen, and the buttons will not respond. if you press the power key, it will automatically restart.
Please help me!