The Pattern Library is part of GenerateBlocks Pro. It’s a separate plugin from GeneratePress Premium. You’ll need to have GB Pro to have access to this feature.
It is possible to copy and paste free patterns from https://generateblocks.com/library/ though, without having GenerateBlocks Pro. You’d need it for the patterns marked “pro” but not the free ones.
Yes, thank you for mentioning that Janeb! You can click on copy for the free ones through that link, and then do CTRL + V or Command + V to paste it on the Block Editor.
As for having the Pattern Library Block, it’s only available in GB Pro.