rqt Plugin Tutorial Not Working

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Hello - I am new to ROS. I followed this tutorial to create a rqt_mypkg python plugin. I am using Ubuntu 20.04 and ROS Noetic. After completing the tutorial, when I run the plugin with 'rqt --standalone rqt_mypkg' I get the following errors:

QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-public'

qt_gui_main() found no plugin matching "rqt_mypkg" try passing the option "--force-discover"

As I followed the steps in the tutorial, I coped the contents of each file from the tutorial and pasted into files on my system.

Things I've tried:

• deleted ~/.config/ros.org/rqt_gui.ini
• tried the --force-discover option on the 'rqt --standalone rqt_mypkg' command
• made sure to run source <workspace>/catkin/devel/setup.bash (actually it is in my .bashrc plus I manually ran the command)
• 'rqt --list-plugins does not list my rqt_mypkg plugin
• when I run 'rqt', the GUI pops up but I don't see rqt_mypkg anywhere in the menus
• the command 'rosrun rqt_mypkg rqt_mypkg' gives an error: "[rospack] Error: package 'rqt_mypkg' not found"

UPDATE #1: Do the errors have to do with my directory structure?

There is an existing ROS package in /home/user/ros. I can run catkin_make in /home/user/ros to compile and build that package. When I started the plugin tutorial, I did Step 1, the catkin_create_pkg command, in /home/user/ros. So I now have /home/user/ros/rqt_mypkg. I followed the tutorial exactly and all my rqt files are in /home/user/ros/rqt_mypkg. If I try to run catkin_make in /home/user/ros/rqt_mypkg, I get the message seen below, so instead I run catkin_make in /home/user/ros:

Base path: /home/user/ros/rqt_mypkg The specified base path "/home/user/ros/rqt_mypkg" contains a package but "catkin_make" must be invoked in the root of workspace

Is it correct that I created the the new plugin rqt_pkg underneath the ros project?

UPDATE #2: This is my current directory structure. The original workspace "ros" which is a fully functioning project that I am just trying to add a plugin to. 'rqt_mypkg' is the directory structure I added as I was doing the plugin tutorial.

ros/
   build/ 
      lots of files in here
   devel/
      lots of files in here
   src/
      CMakeLists.txt  (toplevel CMakeLists.txt for a catkin workspace)
      project1/
         CMakeList.txt (for the project1)
         package.xml
         x.launch
         src/
              project1.cpp
          include/
               include.txt
   rqt_mypkg/
       CMakeLists.txt (for the rqt_mypkg plugin)
       package.xml
       plugin.xml
       setup.py
       resource/
            MyPlugin.ui
       scripts/
            rqt_mypkg
       src/
            rqt_mypkg/
                 __init__.py
                 my_module.py

UPDATE #3: Some progress - thank you! Per your suggestion, I moved rqt_mypkg under ros/src directory. Now when I run catkin_make, I see it is getting compiled as I see these type of statements:

 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 -- ~~  traversing 2 packages in topological order:
 -- ~~  - rqt_mypkg
 -- ~~  - project1
 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 -- +++ processing catkin package: 'rqt_mypkg'
 -- ==> add_subdirectory(rqt_mypkg)

But when I run 'rqt --standalone rqt_mypkg --force -discover', I still get the same error:

qt_gui_main() found no plugin matching "rqt_mypkg" try passing the option "--force-discover"

When I run 'rqt --list-plugins' my ... (more)