Years ago I had an Elvui package. I since got rid of it; however, some interface windows on blizzards default ui never went back to normal. I tried taking screen shots to give examples of what’s wrong but I says I can’t post links. Most every window has a similar issue. The top edge that has that gray bar at the top is invisible, but there are black lines. The esc menu is black and has two vertical lines cutting through it. The character select menu (before entering the game) the enter world button is black and has a vertical line going through it.
I had this Elvui pack years ago, I also removed it years ago. I have just been putting up with the after effects. Since then I have quit and restarted playing numerous times, So the game has been uninstalled and reinstalled several times. Each time these same issues persist. https://imgur.com/5Anm9ZG https://imgur.com/FHXKj7u https://imgur.com/fiDX8In
Wrap them in code tags (</> button in the editor).
Addons can’t run on the character select screen. It sounds like either you’ve got corrupt game assets or an issue with your video card. I’d start by running the Scan and Repair tool: https://us.battle.net/support/en/article/7655
ElvUI is removed when you remove the addon from your Addons folder. Depending on what options you chose during the Setup Wizard it would have also modified some CVars. You can reset all your CVars to default with the following command (this is not reversible):
Check under the Interface folder (below the game version folder) and make sure it contains only one folder called AddOns.
If you have folders in there with other names, move them to somewhere else and start the game.
You could move them all and the game will create a new empty AddOns folder that you could move any addons back in to once you’ve check the result of just having the default.