BoltBait

Make your selection and press Ctrl+X
Press Ctrl+Shift+V
Move your selection around and when it's where you want it, press Ctrl+M

Try pressing Ctrl+Shift+F8

If you have my plugin pack installed, try this:
 
1. Add a new layer
2. Select that layer as the active layer
3. Effects > Fill > From File...

Did you try Ctrl+Shift+F8?

An "Object" is a set of pixels surrounded by transparent pixels.  Your image has no "objects" as you have no transparency.

When Rick says your OS is 5 years old, he means you're missing 5 years of security patches.  It's dangerous to even surf the web with such an OS.

First, select the object you wish to outline, then:
 

The plugin has been published:
 
BoltBait's Text Fun Factory v1.0 - Updated October 29, 2023 - Plugins - Publishing ONLY! - paint.net Forum (getpaint.net)
 
Enjoy!

F8 closes and reopens the window.
 
Ctrl+Shift+F8 will RESET the window to default size and location.

You have the background layer selected, that's where your pasted graphic is going.  You can't see it because it is being covered by an image above it in the layers list.

Try this:
 
Select the magic wand.
Switch the Flood Mode to global.
Click on the color you wish to remove.
Press the Delete key on your keyboard (not the backspace key).

Yes.

After running the stencil effect, apply the Effects > Noise > Median effect.

If you have my plugin pack installed:
 
https://forums.getpaint.net/BoltBaitPluginPack
 
After using the magic wand, use the Effects > Object > Feather

No, but what you can do is find a "Paneling" plugin, apply it on one layer, then select each other layer (one at a time) and press Ctrl+F to redo the effect on that layer.

Sounds like you have an existing paint.net installation that has become broken. Please use this utility to remove the broken installation:
https://support.microsoft.com/en-us/help/17588/fix-problems-that-block-programs-from-being-installed-or-removed
 
Afterwards, you should be able to install paint.net anew.
 

I'm going to guess that this is the reason for your problem.

Step 1: Select the area you want to affect
 

Step 2: Add a new layer by pressing Ctrl+Shift+N
 

Step 3: With black and white selected, press Shift+Backspace to fill the selection with white
 

Step 4: With the shape tool, select Ellipse and fill
 

Step 5: Draw (in black) your circle
 

Step 6: Click the checkbox to turn off visibility of Layer 2
 

 
Step 7: Select Layer 1 (your original image) and run the Effects > Object > Apply Mask plugin (You do have my plugin pack installed, right?!)
 

 
Make sure "Invert mask" is checked and click the OK button to finalize your image.
 
Now, turning that square frame into a circle shape is going to be a challenge.  Try one of these Polar plugins:
 
https://forums.getpaint.net/PluginIndex?keywords=Polar
 
 
 

Click the Ignore button and it will install the plugins for the store version.

Have you tried the built-in Effects > Color > Quantize
 

That may be what you're looking for.
 

More (or less) nubs is a feature that is being DESIGNED right now.  Once a design is finalized it will be developed. So, don't hold your breath, but it is eventually coming.
 
EDIT: Less? Sure, 2 points would be a straight line, 3+ would be a spline, and 4 would be a Bezier.

Why do you need multiple instances?  You can open multiple images in Paint.NET:
 

You can see the thumbnails at the top of the UI.
 
Use Ctrl+Tab to cycle through those images.
 

Try pressing Ctrl+Shift+F8

That's never gonna happen.
 
Here's what @Rick Brewster said about the issue:
 
 
His quote is about JPG instead of PNG, but the same reasoning applies to your question.
 

Sorry, not possible.
 
However, you can always click on the menu:
 

 
Not possible.  Effects are not tools and there is such thing as a tool plugin.
 
 
What would you change them to?