No, it is not possible to connect the Galaxy Tab A9+ directly to an external monitor via a USB-C to HDMI adapter. The Galaxy Tab A Series, including the Galaxy Tab A9+, does not support video output via USB-C to HDMI adapter.

To connect to an external monitor, alternative solutions such as a DisplayLink dock with the corresponding app or other special adaptations would have to be used. The official Samsung USB-C to HDMI adapters and cables are mainly designed for the Galaxy S and Note Series and some Galaxy Tab S models, not for the Tab A Series.