Starting with ColorOS 7 the Intelligent Sidebar (formerly Smart Sidebar) offers the possibility to set the transparency of the bar.

Android 10 (ColorOS 7.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Convenience tools
Step 3:  Tap on  Smart Sidebar
Step 4:  Move  Slider  to adjust the Floating Bar Opacity
  1. Open the Settings
  2. Tap on Convenience tools
  3. Tap on Smart Sidebar
  4. Move Slider to adjust the Floating Bar Opacity

Oppo Instructions
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