If Rambox cannot access neither your camera nor microphone, and cannot share screen, it means that it doesn't have permissions for those actions. Rambox should prompt for them, but if somehow this didn't happen, or the permissions were denied, you can manually set up access by following these steps.

Windows:

1- Go to Start  > Settings  > Privacy > Microphone. In “Allow access to the microphone on this device”, make sure access is turned on.

2- Then, enable the option "Allow apps to access your microphone".

3- Below, find “Allow desktop apps to access your microphone” and make sure this option is turned on.

4- Repeat steps 1 to 3 for camera access.

macOS:

1- In the top-left corner of the Mac Desktop, click Apple menu, then select System Preferences. 

2- The System Preferences window appears. Click the Security & Privacy icon.

3- The Security & Privacy window opens. Click the Privacy tab. 

4- In the lower left of the window, click the padlock icon to make changes. Enter your Mac's administrator username and password. 

5- Click the Camera section. Check the Rambox checkbox.

6- Click the Microphone section. Check the Rambox checkbox.

7- Click the Screen Recording section. Check the Rambox checkbox.

8- Close the Security & Privacy window.

9- Restart Rambox to enact these changes.