A free app for Android, by RealVNC Limited.

The VNC Server app allows you to connect to a technician to support remote users. They can remotely access your device to help you with your technical issue. It provides two ways to connect: The first is to use a secure, predefined code that the technician provides to the user. The second is to use a VNC® Connect Enterprise Device Access subscription to authorize a device managed by the MDM tool.

We know you may be keen on the idea of another person accessing your device, but the program ensures your privacy with end-to-end encryption on all remote sessions. It also requires your connection approval to protect you and your data from unwanted access.