In Minecraft Beta 1.21.120.21 on Android (Xiaomi Redmi 9, Android 10), I found a bug:
When I place a block, sometimes it becomes transparent.
It looks like a ghost block and does not render correctly.
This happens near water and grass blocks.
Environment
• Device: Xiaomi Redmi 9
• OS: Android 10
• Game Version: Minecraft Beta 1.21.120.21
• Renderer: RenderDragon
Please update to the latest Beta (1.21.120.23) and see if the issue still occurs.