I am creating a new project and I encountered this problem.

Board type - ESP32 WROOM
Display type - Riverdi 4,3" with SSD1963 parallel 8bit driver

My test project is here.

Project created wit Square Line Studio.
Settings is:
Resolution: 480x272
Depth: 16 bit swap

View created in Square Line is

The real display is

In which setting could there be a problem?

you typically only need the color swap if using an SPI interfaced display. I would try turning that off. The display might also be in 24bit mode which LVGL doesn’t support. It supports 16bit and 32bit. so if it is in 24bit mode you either need to iterate over the buffer in the flush function and remove the alpha channel or set the display to 16bit color and LVGL to 16bit color

The display connection is parallel 8 bits and the color depth is 16 bits. SSD1963 driver supports 18 bits. What would be the best solution? Can this problem be solved at all?

The driver ic supports the following

16 lane: RGB888
16 lane: RGB565
12 lane: RGB888
9 lane: RGB565
8 lane: RGB888

so if you have it set to 8 lane mode and you have the color depth set to 16bit that is incorrect. LVGL doesn’t support 24 bit color frame buffers it goes from 16 bit to 32 bit. You would have to write a custom flush function to strip out the 8 bits (alpha) to make it 24 bit to send on 8 lanes. You can use an additional pin and set the IC to 9 lane mode using command 0xF0 and writing 0x06. Then you can use 16bit color depth. I believe you need to have the byte order set to BGR565 for that driver IC.

This is the data sheet for the driver IC pages 17 and 78 cover the bit depth/number of lanes and how to set it.