Need to use 0.1 or max 0.15 mm thick PCB and even then it is challenging as max height PCB with components is limited to 0.7mm.
#UD Card with ICE65 FPGA was old attempt where the components are outside the normal micro SD Card area. Today it is possible to push the components into the real form of micro SD.
Body height: FPGA 0.45mm OK, Serial Flash 0.41mm OK. The remaining parts should be OK too.