Hi Chang,
WPSP was merged with GenerateBlocks, not GeneratePress. 🙂
The GB Query loop block can retrieve related posts.
With regards to related posts, you can build related posts in GenerateBlocks Pro 1.3.0 (currently in alpha) and GB 1.5.3.
Otherwise, you’ll need custom code. See this thread for more info with regards to this: https://community.generateblocks.com/t/use-gb-query-loop-for-related-post/688/27
Hope this clarifies!