You need to set the base directory to nft-minting-app-main as per Build from a subdirectory or monorepo documentation (because the code you wish to deploy is in the directory nft-minting-app-main inside the repository.) The publish directory accordingly needs setting to nft-minting-app-main/build as build is the location CRA builds to.
CI= npm run build is only necessary if you as wishing to set CI to false (which ignores warnings. ) For most builds npm run build works.