I thought so, too.
But how would you explain this:
I have a simple PL2303 USB-RS232 interface. I connect 4 pins: 3.3V, GND, TX and RX to the "Multiboard", which is acting as a standard ESP32 SOLO with a SD reader soldered to it (using CS, CLK, MISO, MOSI, 3v3 and GND). I open a terminal program (SmarTTY) and I can see the ESP32 boot to Marauder and the SD is recognized, as well as the files it is looking for.
Now I take the exact same "Multiboard", connect it manually using the same wires I used on the test before and connect them to 3.3V, GND, TX and RX of the Flipper (it offers a series of pins, including these). On the Flipper, I activate an app, that just forwards the TX/RX communication to the same terminal program (SmarTTY). Now the ESP32 boots just like before, but it fails to mount the SD.
Everything is the same, the Flipper is just powering up the ESP32 and provinding a RS232 to USB interface functionality, which works, since I can see the whole CLI messages of the Marauder software running on the ESP32.
The only difference is that the PL2303 offers 3.4V, while the Flipper offers 3.2V. I cannot find any other difference.