Hi there,
The GB Headline Block cannot display static text and a dynamic link, both have to static or dynamic.
But if you use a GenerateBlocks Button Block then that you can set some static text for the button label, whilst setting Dynamic Link > Post Meta –> Your ACF field name, i would probably set a URL field in ACF.
Note: When you add the Button you must give it a static link – simply add #
– this is required for GP to swap it for the dynamic link.