Hi there,
The login or register can be added using a block element – hook, choose menu_bar_item as the hook name.
You can add a container block, then insert a button block with the login link and a headline block with the text “or”, then another button block with the registration link.
The 2 button blocks and 1 headline block needs to be set to display: inline-flex or inline-block.
https://docs.generateblocks.com/article/layout-options-overview/#inline-block
https://docs.generateblocks.com/article/layout-options-overview/#inline-flex
GP doesn’t have a built-in function for the pop-up windows, you will need to look for a plugin which does this.