Brick Wall: AI Adoption Case Study

My great grandmother whose initials are B. F. C. ( March 1927-June 25th 2000) was adopted I can’t find her bio parents. We often suspected Mediterranean blood, like some type of North African or perhaps Arab based on her phenotype so I took a DNA test and got very distant (3rd-4th marches) on that side that appeared Mediterranean, found out they’re predominantly Spanish , Cuban, Mexican with traces of Taino and North African from Canary Islands. Yet I still can’t connect them to my tree. So I then got my grandmother to take a DNA test and she had some North African, Greek, Spanish and so much more in her I feel that may hint at her bloodline. I suspect possible Cuban ancestry really but I’m not sure and since it’s distant it’s harder to pinpoint. My goal is to find her true ancestors I can’t find adoption records. What is the best way for me to proceed to find my great grandmother's biological parents?