Yes, Vivo S1 has an in-display fingerprint scanner.
Yes, Vivo S1 has dual 4G VoLTE support.
Vivo S1 has 6.38 inches of AMOLED Full HD plus display. It is further protected with Corning Gorilla Glass 5 level of protection. The mobile has a 90% screen-to-body ratio and has 19.5:9 aspect ratio. Vivo S1 offers 404 PPI of resolution.
No. Vivo S1 does not have the 5G network support. It works on 2G/3G & 4G GSM networks.