Oh I see, there are two ways you can improve how it splits text:
1. Add line-breaks where you want them
2. Disable "Font size auto-fit" and set another font-size so that the text breaks at the right place. By default the editor makes the text as big as possible to fill the layer, but you can disable this "auto-fit".
If you're talking about this tool: https://www.generatebanners.com/free-open-graph-image-generator then there is no way to add line breaks indeed.
However if you do log-in into https://www.generatebanners.com/ then this feature is available (using the logged-in version is also free and much more complete than the simple demo).