Is there any virtual webcam on Android that can remove the background?

The Android framework has no exposed APIs for third-party plugin app camera filters.

If a third-party program can inject itself into the Camera API, it would need to read the image data, if it can read the image data, it could exfiltrate the image which would be a security issue.

Applications themselves provide any visual features generally with OpenGL shader code or a ML pipeline.

My only suggestion is to submit feedback to the various Android apps the need for such a feature.

For an example of the complexity to developers see my answer to taking a picture with a Depth of Field camera.