is your RTX card a 30 or 40 series? PNGTuber Plus uses OpenGL, however newer graphics cards have been lessening their support for OpenGL in favor of Vulkan. This means some newer cards that you'd expect to run something like this very well struggles. OpenGL works better for most people which is why it was selected. Some rtx people don't seem to have this issue however, it could just be laptop rtx cards only, unfortunately I don't have the technical know how to say for certain.
You can download the source code for pngtuber plus and swap it to vulkan, however there are no promises everything will work correctly