- Type letter ‘c’ using the text tool, as you’ve already done
- Create a new layer from text
- Duplicate layer
- Transform - flip horizontally
- Merge two layers
It’s a basic GIMP knowledge, really. Don’t forget to add an alpha channel to your layer after step 2, otherwise it won’t work.
Sometimes I’m searching for a recipe to some obscure Linux tool and finding my own answers on Stackoverflow from ten years ago.