A Spacer Block will add space between blocks. The right sidebar has space to enter the height in pixels, or you can click the blue dot at the bottom edge of the space box and drag it to the desired size.
TO ADD SPACE BETWEEN SENTENCES
When you type text into the post or page and click Enter, a new paragraph block appears. To avoid creating a new paragraph while adding space between sentences, hold the Shift key down, and then press the Enter key.