The study is a Phase III, randomized, multicenter, open-label study in HER2-low, HR+ metastatic breast cancer subjects who are patients with locally advanced or metastatic breast cancer with low HER2 expression in the recurrent metastatic stage who have not received chemotherapy. The primary objective of the study is to determine the efficacy and safety of TQB2102 compared to investigator-selected single-agent chemotherapy in the target population. 542 subjects with HER2 immunohistochemistry (IHC )2+/ in situ hybridization (ISH)- and IHC 1+ (HER2-low) expression will be enrolled in 1:1 randomized groups to receive TQB2102 or investigator's choice of single-agent chemotherapy (capecitabine, paclitaxel, or albumin-paclitaxel) until progression of disease (PD), as defined by Response Evaluation Criteria in Solid Tumors (RECIST) 1. 1, unless there are unacceptable toxicity, withdrawal of consent, or meeting other discontinuation criteria.