so, added more colors and theme set on all screens for all components, now the ESP32-S3 does not start, it goes bootloop. Here is the coredump:
ELF file SHA256: 2594c914f41883b2
Rebooting...
ESP-ROM:esp32s3-20210327
Build:Mar 27 2021
rst:0xc (RTC_SW_CPU_RST),boot:0x9 (SPI_FAST_FLASH_BOOT)
Saved PC:0x40377d34
SPIWP:0xee
mode:DIO, clock div:1
load:0x3fce3808,len:0x44c
load:0x403c9700,len:0xbd8
load:0x403cc700,len:0x2a80
entry 0x403c98d0
E (12316) task_wdt: Task watchdog got triggered. The following tasks did not reset the watchdog in time:
E (12316) task_wdt: - IDLE (CPU 0)
E (12316) task_wdt: Tasks currently running:
E (12316) task_wdt: CPU 0: loopTask
E (12316) task_wdt: CPU 1: IDLE
E (12316) task_wdt: Aborting.
abort() was called at PC 0x42046188 on core 0
i do not know why this is happening… do you have any idea?
update: i tried to add the theme 1 by 1 to the screens, and it seems for 1 screen with 8 components the ESP32 starts smoothly. For 2 screens, the main screen starts but then goes to bootloop. So, does it something with watchdog timers? It could not reset it because switching to themes took so long, that is why the restarts?
update2: commented out ui_object_set_themeable_style_property seems solves the problem - the esp32 starts - but with default global theme on the widgets and components. So no theme switching, still… And this reminds me the following bug here on this forum: Themes Drastically slowing down Screen/Component Generation
but in my case, setting LV_SQUARELINE_THEME__OBJECT_VALIDITY_CACHE does not solve the problem 
My company had high hopes in this theme switching function though…