BBEdit uses Mac OS system to highlight text. Using a pointing device, you can click and drag over a block of text. You can also double click a contiguous block of characters. You can triple click a “paragraph” of text.
With the keyboard from the insertion point, hold the shift and an arrow key, modifying that movement with the command or option key.
If your goal is to highlight some text and have it stay that way as you’ve done in this email, what you want is a word processor, not a text editor. BBEdit is a magical text editor, not a word processor.
Sorry if this doesn’t give you the answer you wanted your question.