Well, it seems to work. All I had to do was selecting the GPIO pins for the SPI bus and setting the correct defines (ESP32 for the microcontroller and EVE_PH800480, plus a bunch of size and sync settings for the display).
For my specific display, I added these at the beginning of EVE_commands.cpp:
#define EVE_HSIZE (800L) // 800 x 480 px
#define EVE_VSIZE (480L)
#define EVE_VSYNC0 (0L) /* Tvf Vertical Front Porch */
#define EVE_VSYNC1 (10L) /* Tvf + Tvp Vertical Front Porch plus Vsync Pulse width */
#define EVE_VOFFSET (23L) /* Tvf + Tvp + Tvb Number of non-visible lines (in lines) */
#define EVE_VCYCLE (525L) /* Tv Total number of lines (visible and non-visible) (in lines) */
#define EVE_HSYNC0 (0L) /* Thf Horizontal Front Porch */
#define EVE_HSYNC1 (10L) /* Thf + Thp Horizontal Front Porch plus Hsync Pulse width */
#define EVE_HOFFSET (46L) /* Thf + Thp + Thb Length of non-visible part of line (in PCLK cycles) */
#define EVE_HCYCLE (1056L) /* Th Total length of line (visible and non-visible) (in PCLKs) */
#define EVE_PCLK (2L) /* 60MHz / REG_PCLK = PCLK frequency 30 MHz */
#define EVE_PCLKPOL (1L) /* PCLK polarity (0 = rising edge, 1 = falling edge) */
#define EVE_SWIZZLE (0L) /* Defines the arrangement of the RGB pins of the FT800 */
#define EVE_CSPREAD (0L) // was 1L
#define EVE_TOUCH_RZTHRESH (1200L) /* touch-sensitivity */ // was 1800L
#define EVE_HAS_CRYSTAL
#define EVE_GEN 2
#define EVE_CFAF800480E0_050SC // touch controller
I noticed that my voltage regulator, that brings the 24V supply down to 5V for the backlight, is overheating when I set the backlight to 100%.
But for the rest, everything works as expected.
@newbrain: Thank you for guiding me to the exact line in the code!

I'm just getting started with these smart displays. My next step is to play around with the EVE Screen Designer application provided by FTDI.
I believe that will make the GUI design a lot easier.
P.S.: Sorry for the not so fast reply. I'm only playing around with this from time to time