Do you mean with internal content (ie. apps running on the projector itself) or external content (HDMI / USB-C)? With internal content, it should already work. If it doesn’t for you, there should be help available with that here on the forum. With external sources, it’s unfortunately never going to work because the hardware doesn’t support it. The 4 corner adjustment is part of the projector’s Android OS, and the external sources bypass that completely. See this thread for more info: INFO: Limitations of features for HDMI and USB-C inputs
Edit: sorry, just realised that you probably asked very specifically about the linearity issue and not about 4 corner correction in general.