If you want, tell me the exact X20 Mini model string (from About phone or printed on the device) and I’ll provide a targeted install plan and links to likely recovery/ROM sources.
Depending on the specific custom build you downloaded, the installation happens in one of two ways: x20 mini custom firmware full
A: Yes. Flashing firmware is a low-level operation that typically wipes all user data. Back up everything important before you begin. If you want, tell me the exact X20
TriForceX/MiyooCFW: Custom firmware source code ... - GitHub If you want
Change the display scaling from "Stretch" to "Core Provided" or "4:3" to eliminate stretched, distorted pixels on the screen.