Hi @wisdomtogbe
It could be that the battery has failed or that the there's a problem with the USB charge port board so that the battery can't be charged and as become depleted and the phone cannot be connected to a computer etc.
Here is a composite image from the [document|29533|troubleshooting] guide from the service manual that may help. There are also images in the guide which show the location of the parts mentioned in the flowchart.
They show the path to follow to test if all is OK or not
[image|3006717]
(click on image)
Here's the ifixit [[Topic:Samsung Galaxy S21]] guide that will help you to access the components in the phone.
If you find this a bit daunting, contact a reputable, professional mobile phone repair service and ask for a quote to repair the phone.