I assume with "SS" pin you mean the signal connected to the CSB pin of the sensor.
(I did a quick scan of the document provided and I could not immediately spot an SS pin.)
The SS/CSB pin is an input and your micro-controller's SPI interface must set it low in order to access the device. If it does not go low that is not an error of the sensor. You should sort out your micro-controller SPI interface.
The MISO pin will only be active if the SS pins goes low. Thus until you have sorted out the above problem the MISO pins should be tri-state.
As to them being always high: there may be a pull-up but, in contrast to I2C interface, the SPI interface normally does not use pull-up resistors.
ESP32 is not able to set it low.
Where did you get that from? I am struggling to find a full datasheet for the ESP32 to look up the details but what I did find is a summary of the ESP 32 where it says:
"ESP32 features three SPIs (SPI, HSPI and VSPI) in slave and master modes"
The sensor is an SPI slave device. The only way to communicate with it, is using the ESP32 in SPI master mode. An SPI master must drive the chips select (or slave select) low in order to communicate with the chip.
Again: If your SS does not go low that you should check what is wrong on the ESP32 side.
Maybe something is set wrong with pin mode or pin multiplexing or GPIO settings or with using the SPI in master and not in slave mode...
I know these things are hard. I once took two days to find out how to configure the GPIO pins for a UART2 on an Atmel chip.