After recreating User_setup.h from the original TFT-eSPI version, I have managed to resolve this. After comparing it to my original post, I dug a bit deeper.
It seems this will fail as described in my OP if TFT_MISO, TFT_MOSI and TFT_SCLK are not explicitly defined in User_setup.h. It is unclear why this is an issue, as the pins I am using match the VSPI pins for this board.
Note that with the failure mode in my OP, SD card access will be unavailable via the SdFs interface and unavailable to LVGL image creation (via lv_image_set_src() ).
Thanks for your attention.