In the old days you could bypass system calls, bios calls, etc. by writing an ASCII character directly to a byte in the "screen buffer". Is there something similar with the raspberry pi 4b?
Strictly speaking, no. The video output of the Pi is under control of the VideoCore, not the ARM CPU.
You can allocate a framebuffer and use low-level memory writes to fill it, but you'll still have to talk to the the VideoCore to get it displayed.
In a less strict sense, you could consider the VideoCore as an equivalent of the VGA adapter hardware. It's a question of what you would be willing to call "direct access".