Thank you very much, macropod, for your help!

To give you an idea of how the toggle buttons I use work, they are essentially the same as the buttons for aligning a paragraph (right, center, left, or justified). Only one of these buttons can be selected at a time.

The solution to this problem is not to save a table in a Building Block, but rather to use and adapt a simple text paragraph and surround it with borders... (see Home tab > Paragraph group). In this case, only one toggle button is selected at a time.

Thank you all!

Best regards,
David