Yes, Oppo A71s does have the OTG support.
Oppo A71s has 5.2 Inch HD IPS with 1280 x 720 resolution. The display offers 282 PPI ratio. The display has 2.5D curved glass but unfortunately, it does not have any kind of display protection.
No. Oppo A71s does not have the fingerprint scanner.
Yes, Oppo A71s has the FM radio.