You'll need to identify the device node representing the card. Understanding the difference between a block device, a device partition, and a filesystem is probably a good thing at this point. The device node is not a mount point. If there are no other storage devices attached to the Pi, it will probably be /dev/sda. Note for emphasis in case you did not ...
the green LED is blinking 4 times and pauses and blinks again and continues this step.
As you have seen this indicates a boot problem, namely that "start.elf is not found".
Didn't find any docs on how to resolve it.
I imagine that is a bit inscrutable if you don't know what it is referring to. start.elf is required to be in the boot partition, which is ...
You will not get anything at all until the Pi4B has successfully booted.
Your Pi4B has not booted successfully.
Go through this Pi4B specific boot sticky.
If that does not resolve the issue go through the full boot sticky.