How to develop GUI application without using Qt

Qt is too heavy.
I have downloaded the arm cross compiler, and the helloworld runs ok.
I found in /usr/lib
I asked chatgpt a demo of libwayland
Now I only need header files of libwayland, but I couldn’t find

I think you should build a SDK (Linux SDKs | Toradex Developer Center) containing toolchain + libraries/headers.

Yes, I got a pre-compiled SDK, and there are headers and libraries in the rootfs. I have successfully built and run a QT demo.
Still need to figure out building an SDK by myself.

As mentioned above, by bitbake <image_name> -c populate_sdk , you will build the SDK for the image.

I download a bitbake, but when I run this command, bitbake reports an error: BBPATH not set. Could you give me a guide of installing bitbake.

The bitbake tool itself doesn’t work. You need to prepare all recipes for Yocto Project. Here is the guide for our reference image and the SDK as well.