I saw some videos regarding raspberry os installation on virtual boxes, but now if I connect my raspberry pi 4 without an SD card in it, will it work?
Welcome to the forum!!
The uSD card stores the operating system so unfortunately you’ll still need one with the OS installed so you can boot it up!
PS: RPi foundation have released a new bootloader so you can install your OS of choice without another computer (you’ll still need one to put the new beta bootloader on there at present), check out this video from Gary Explains: Boot and Install Raspberry Pi Over Internet - No SD Card Needed! - YouTube
Thank You Liam