golang. Self-written package is not visible from the main module?

Question

go

Started learning Go and just can't beat a simple problem.

Go 1.16

In accordance with the examples, I do this:
1. Set GOPATH = c:\projects\go
2. In the c:\projects\go folder I create the src subfolder
3. In the scr folder I create the mytest directory and folders, I get the following structure:

src\ mytest\package1
src\mytest\cmd

4. In package1 I create a package1.go file:

package paсkage1

// RetVal test function
func RetVal() string {
  return "passed"
}

5. In cmd I create the file main.go

package main

import (
  "fmt"
  "mytest/package1"
)

func main() {
  fmt.Println("Test of package:")
  fmt.Println(package1.RetVal())
}

When I try to execute the code with the go run main.go command, whatever I do, I get an error:

main.go:5:2: package mytest/package1 is not in GOROOT (c:\go\src\mytest\paсkage1)

Why doesn't main.go see this package? In videos on YouTube, everything works for people.
I do 1 in 1 like they do - it does not work.
Copying examples from the Internet - does not work.
I can't figure out what's wrong.

It works only if you copy it to the system folder c:\go\src\mytest\package1
I don't want to clog the system folder, and plus then the question arises of how to add such code to git.

Answer 1

Either get an old version of Go like the youtubers have, or finally start using go modules .