1) You need to use the patched boot image for the firmware version installed on your Mi A2 Lite. So, if you have V10.0.3.0, you will need to use the patched V10.0.3.0 boot image.
2) Yes, you need to enable OEM unlock in Developer Options and also unlock the bootloader after that. You can find the guide for unlocking the bootloader on Mi A2 Lite here.
From: Scott on Android Forums
In a nutshell: It gives you access to all partitions. You can change everything, not just boot/system/recovery,like our current setup.(S-On/UnLocked)
Lots of folks like to change splash images and radios,wich you cannot do with our current unlocked S-On arrangement.
You can also go backwards in build numbers, and run older ruus. So if you were S-Off, and flashed the leaked ICS RUU and didn't like it, no biggie. You can revert back to gingerbread radios, hboot, software, etc. By simply running an older, GB RUU. You can even go back to original shipping firmware.
Because you can flash literally anything, you do have a bigger responsbility to be informed about what your doing, what you're flashing, and why. Double and triple check the integrity ofanything you flash by verifying md5 sums, as flashing a bad bootloader or radio will leave you withan unrecoverable, hard bricked device.
It will also let "boot" be written from recovery, making the seperate kernel flashes we do now un-neccessary (as soon as devs build their ROMs to flash the kernel from recovery)
It is my opnion, that S-Off is better, as long as caution is used in flashing, as it gives you more options to recover a soft brick. You can easily install an eng hboot(wichwill offer extra fastboot commands), install a recovery, or run an older RUU.
S-On or S-Off is describing the status of the radio secure flag. Basicallyits "Security On" or "Security Off". Since it is housed in a location seperate of all other partitions, you will stay Security Off no matter what hboots or RUUs are flashed, until you purposely change it.
Oh... almost forgot
Big thing most folks are excited about(I dont really care, as I have no MFG warranty) is the fact that an S-Off phone can change the relocked status back to shipping status of locked and then the security turned back on, thus fooling HTC/VZWthat any unlocking trickery has occured, and preserving your manufacturer warranty if you need it
Last and not least, if none of these things appeal to you, nothing wrong with staying UnLocked S-On. It does add a degree of safety, as the S-On hboot will onlyflash newer, HTC signed files, making it nearly impossible to brick by flashing bad firmware.
Hope that helps
Download File https://oyndr.com/2yXWW9