Hello Ogün Levent,
You can find the number of GPIOs available on the i.MX6SX in its datasheet (link below). There are seven GPIO banks, however, most of these pins are not dedicated, which means that the amount of available GPIOs will be affected depending on how many of the available modules and interfaces you would be using.
https://www.nxp.com/docs/en/data-sheet/IMX6SXCEC.pdf
My recommendation would be downloading the Pins Tool for i.MX to work out the pin muxing for your design and determine if you may be able to accommodate all your interfaces plus the fifty required GPIOs.
https://www.nxp.com/design/designs/pins-tool-for-i-mx-application-processors:PINS-TOOL-IMX
I hope this helps!
Regards,