There's only one way to remove encryption and it requires to format data(formate everything incl. Internal storage)
Steps:
1) Remove all ur accounts from device especially mi account(first turn find device in it off), Google account and all other accounts associated with it.
Also remove all password including fingerprint, face unlock, screen lock etc.
2) Go to developer options & turn usb debugging on.
3) copy "disable force encryption" zip file and magisk latest version in "external SD card"(not in internal storage)
4) go to twrp> wipe> advanced wipe then click on "format data" on lower right corner, now type "yes" and swipe right.
5) go to twrp>install> choose storage as ext. SD card and flash "disable force encryption" zip file then magisk.
6) Reboot to system.
I mentioned all steps I could remember, sorry if I have missed something. Further try any YouTube video for help and easy step be step video guide.
Try at ur own risk