Unable to get into the GUI after installing a NVIDIA driver via apt - still can't get in after the driver uninstalled

Question

My laptop has an Intel and a NVIDIA video card, when I installed I chose to use a NVIDIA close-sourced driver, and it works.

Today, after I installed nvidia-driver-390 with apt, I can not get in the GUI after reboot.

After booting, the Ubuntu logo can be seen, but then the monitor went all-black, with an _ underscore jumping at the left-top. After several seconds the monitor refreshes, the _ disappeared, then the monitor refreshes again, then _ comes back, then after several seconds the same procedure loops.

It is possible to get in to the terminal with Ctrl+Alt+Fn, but after several seconds I will be transferred back to the not-working GUI with that _ jumping, so it is not possible to work on the terminal in init mode 5.

However, it is possible to work in the terminal in init mode 3. I apt remove --purged everything starts with nvidia, rebooted, but everything is the same.

I tried to startx in the virtual terminal, but X just shut down immediately - maybe it is because I am in init mode 3?

I checked the Xorg log, there are several error lines:

(EE) open /dev/fb0: Permisssion denied 
...
(EE) modeset(GO): eglGetDisplay() failed
(EE) modeset(GO): glamor initialization failed

I removed the quiet grub option, and found that the system stuck at:

Starting Show Plymouth Boot Screen...

There are another three maybe relevant operations:

1. After I installed the driver, I opened a 3D game to test before reboot, but the game complains that there are some OpenGL problem so it won't start.

2. Before installing from apt, I installed the .run driver released by NVIDIA co., but the installation failed for that nvidia-drm kernel module not found. I just tried run the .run with --uninstall, and it says there are no NVIDIA drivers currently installed.