This is a parallel group, Phase 3, multinational, multicenter, randomized, double-blind, placebo-controlled, 3-arm study for treatment of participants diagnosed with moderate-to-severe AD on background TCS who have had inadequate response to prior biologic or oral JAKi therapy. The purpose of this study is to measure the efficacy and safety of treatment with amlitelimab solution for subcutaneous (SC) injection compared with placebo in participants with moderate-to-severe AD aged 12 years and older on background TCS and have had an inadequate response to prior biologic or an oral JAKi therapy. Study details include: At the end of the treatment period, participants will have the option to enter the Long-Term Safety Study LTS17367 (RIVER-AD). The study duration will be up to 56 weeks for participants not entering the long-term safety study (LTS17367 \[RIVER-AD\]) including a 2 to 4-week screening, a 36-week randomized double-blind period, and a 16-week safety follow-up. The study duration will be up to 40 weeks for participants entering the long-term safety study (LTS17367 \[RIVER-AD\]) including a 2 to 4-week screening and a 36-week randomized double-blind period. The total treatment duration will be up to 36 weeks. The total number of visits will be up to 13 visits (or 12 visits for those entering the long-term safety study LTS17367 \[RIVER-AD\] study).