For Vancouver you need to record all authors in your final reference list or bibliography. You can only use et al. if there are 7 or more authors. For example:

6 or less authors, list them all

(11) Inamdar SR, Prevost S, Terrill NJ, Knight MM, Gupta HS. Reversible changes in the 3D collagen fibril architecture during cyclic loading of healthy and degraded cartilage. Acta biomaterialia. 2021; 136:314-26. 

7 or more authors, use et al after 6

(12) Yap TA, Siu LL, Calvo E, Lolkema MP, LoRusso PM, Soria J-C, et al. SARS-CoV-2 vaccination and phase 1 cancer clinical trials. The Lancet Oncology. 2021; 22(3):298-301.