Every window/program that I open, opens on the opposite of my two display screens. Why?

On the Display arrangement screen in the System Preferences, you will see one of the displays showing a menubar while the other ones will be missing the menu bar. It can be hard to see as it is a very thin light gray band representing the menu bar. Just drag that menu bar representation to the display you want to be the main one. This is all done on the Display Arrangement screen within the Display System Preferences.

Edit: I don't have access to Big Sur at the moment, but it should be on the screen where you arrange the monitor positions relative to one another. See the white bar on the left display in this picture:

Have you tried to drag the white bar in system preferences that represents the menubar from the representation of one display to another? In the picture below the red arrow shows what you will be doing is dragging the representation from the top of one display to the representation of the other.

There are 2 utilities I have used to memorize where I want apps to open, position and size windows.

Stay

https://cordlessdog.com/stay/

And Moom

https://manytricks.com/moom/

There is a menu item for memorizing window positions and sizes.

I currently use Moom, but before that I used Stay. Both are paid apps, but they have demo periods.

Both apps are great when you have to disconnect the external monitor as the can memorize window placement and sizes based on monitor configurations.

Apple menu -> System Preferences -> Displays, drag the menubar representation to the other display and see if the behavior is still erratic. If it is, then it is the application and its home display that is controlling where windows are opening up. The home display for the application is typically the window it first opens up in. If you save a document in an open application it will typically remember where it last saved the window location. Using the Option key while clicking the green control lets you force the window to maximize on the display that has the most content of the window.

J Bertram wrote:

Logically, if I select the menubar on the bottom of a particular screen, then what I select to open should open in that screen and not the opposite screen. There would need to be a setting to do that but Apple has not provided one. When I select an app on the menu bar on the Samsung display, the app opens on my MacBook Pro. Conversely, when I bring up the menu bar on my MacBook Pro and open an app, that app opens on the Samsung display.

Also, in preferences, I have my menu bar set to stay visible ("Automatically hide and show dock" in preferences is not checked) yet my menu bar is not visible on either display and I have to take my mouse to the bottom of the display in which I want to see the menu bar. So that preference is not working either. Another preference that doesn't work as stated.

I think you are confusing the menu bar which is the bar at the top of the screen which has all the menus such as the "Apple", "File", "Edit", "View", etc. items.

The bar at the bottom (or on the sides if moved by the user) is the Dock which holds shortcuts to apps & documents. The Dock will move between displays (not sure what triggers it to move). All I know is that you need to move the pointer off the screen at the location of the Dock in order to bring the Dock to the current monitor (this can sometimes be tricky, especially depending on the arrangement of the various monitors & the position of the Dock.

The Dock is where you can launch applications. The menu bar only gives you access to various menu options for an app which currently has focus. The exceptions are the Apple menu and the icons on the right half of the screen which can show the Control Center, Battery icon, WiFi icon, and there may be icons from other apps there for selecting various options (like showing the weather conditions).

As for the moderation, it is hard to say, but most times it will involve accidentally posting personal information (a serial number is considered personal information so it may not always be obvious), or posting on a topic against the forum rules (again, this can cover things not always obvious). Unfortunately we are not always told exactly why the item was edited or removed. Even the forum will sometimes automatically sanitize a single word after clicking the "Post" button (I've seen it happen to normal everyday words). It can be quite frustrating even for regular contributors.