Summary:
Community bug has been reported as seen below.
"In the Bedrock Edition, ravagers can break plant-like blocks, this does not apply to wither roses. mobGriefing was set to true."

Repro Steps:

Create a new World in Creative mode.
1. Place a few Wither Roses and spawn a Ravager next to them.
2. Push the Ravager into the Wither Roses.

Observed Results:
Ravager does not destroy Wither Roses but can destroy other flowers. Please note that Ravagers do not destroy any flowers on Java 1.16.1.