According to your log, you have 2 monitors connected to your machine, both 1920x1080. Nothing like 1536x864. This no monitor resolution.
23:29:08.088: Available Video Adapters:
23:29:08.090: Adapter 0: Intel(R) UHD Graphics
[...]
23:29:08.090: output 0: pos={0, 0}, size={1920, 1080}, attached=true, refresh=59, name=E22
23:29:08.090: output 1: pos={1920, 0}, size={1920, 1080}, attached=true, refresh=120, name=
In case you set Windows to 1536x864, check and activate the native resolution of 1920x1080. In case dialog and text becomes too small, check in Windows settings->Display->Scaling and Layout and set the size from 100% to 125%.
To minimize the GPU load, set your canvas resolution to your output resolution, i. e. 1280x720. This way the internal frame buffer used by OBS for compositing is as small as possible, so processing is as fast as possible.