cannot find package from goroot gopath

Question

if i download external library (ex. go get -u github.com/gin-gonic/gin)

it goes to c:\Users\username\go\pkg\mod not c:\Users\username\go\src

Inside the go\pkg\mod folder, it has external library

i got error like this

could not import github.com/gin-gonic/gin (cannot find package "github.com/gin-gonic/gin" in any of 
    C:\Program Files\Go\src\github.com\gin-gonic\gin (from $GOROOT)
    C:\Users\dusrj\go\src\github.com\gin-gonic\gin (from $GOPATH))

My GOPATH & GOROOT is as follows

go env GOPATH
-> C:\Users\dusrj\go

go env GOROOT
-> C:\Program Files\Go

If I manipulate environment variables in the system window and change GOPATH to the following,

C:\Users\dusrj\go\pkg\mod

error message is changed like this

could not import ...
    ...omitted...
    C:\Users\dusrj\go\pkg\mod\src\github.com\gin-gonic\gin (from $GOPATH))

The weird thing is that sometimes there is no error

Creating an src folder in a C:\Users\dusr\go path and copying and pasting the github folder in it didn't worked for me

go mod init also didn't worked for me

OS: Window10, Go version: 1.17.6 IDE: vsocde

Any help would be highly appreciated. thank U :)