Well, seems too early for this device (there still isn’t a specific section even on XDA), anyway we suggest to start by “doxing” it:
https://www.gsmarena.com/oppo_a77-11599.php
It’s a Mediatek MT6833P/Mali-G57 SoC-based device, so the fastest way is to try GSI:
- https://community.e.foundation/c/e-devices/gsi/88
- [HOWTO] install eOS GSI on a Treble device - new GSI added June 14th
Hope that helps !