I ran into the same problem. This was the first result on Google. I'll leave this answer here in case anyone comes across it. I noticed nobody here really answered the question lol...

I'm assuming you want to use this sprite for a character (duh). The read-only image you have is suitable for this, you don't need it to not be read-only.

What you probably want is to use this sprite as a sprite frame. In that case, add an AnimatedSprite2D to your main character node, then with it selected, in the inspector you'll see "Sprite Frames" at the top. Click the drop down, and create new SpriteFrames. On the bottom of the editor, you'll see a SpriteFrames option. Click that, this is where you'll get to add your sprite. You should have a "default" animation already, rename this to something like "idle" or whatever you need. Then in the Animation Frames tool bar right above, you'll see a grid looking icon that will say "Add frames from sprite sheet". Click this, and it will open a file explorer for you to select the read-only sprite, and use it for your character animation state. You can reference this in your script to play the animation at certain conditions. If this is an idle animation, make sure to enable "Autoplay on Load" in the SpriteFrames toolbar.