I have attached a proper fix for /data partition (or /sdcard or /userdata whatever you want to call it, it's both) not mounting in TWRP and you getting "encryption unsuccessful" problem. It's made from modifying actual fstab of Redmi Go. Simply flash this, and then format the /data partition to EXT4 (you do this by changing the file system to EXT3 (or anything other than EXT4) and then changing it to EXT4 in TWRP). USB flash drives also mount fine with this.
I just flashed your fix, headed to format data partition as you said and found out it was already in EXT4. Is it necessary to format the data partition to EXT4-EXT3-EXT4 if flashing the zip alone serves the purpose?