Posters are single pages to convey information in an attention-grabbing visual! They are slightly different from a Flyer template.
They help to relay information and are most suitable if you plan to later print your work to paper.
For Poster templates, there is no semi-transparent line to adjust the height at the end of the block, so you'll have to use the Settings tab on each block's left border for this.
Can I add a block to my poster?
Sure thing! You can refer to this article here on how to add an additional page/block to your poster.