Install MIUI update with TWRP

Hello

I recently got a MIUI update for my Mi 8 and I was wondering how can I install this update safely

https://piunikaweb.com/2020/05/05/how-to-install-miui-12-update-using-twrp-on-xiaomi-devices-globally/&ved=2ahUKEwjyi6-9i-jqAhWqxoUKHaVXAg0QFjAFegQIJBAB&usg=AOvVaw1KBSz1cB0orKJZhKYL-KVv

https://amp.reddit.com/r/Xiaomi/comments/ael4s3/miui_updates_on_rooted_device_with_twrp_recovery/

Both this redditor and the tutorial use lazy flasher. However on the site, they say that I should wipe my data and my system. Is the data wipe necessary ??

And why do I also have to wipe the system ? Because normally, the update script "patches" the current system...

Thanks for helping (and by the way sorry for my English)

(I am reposting this since I cannot post it in the Xiaomi subreddit due to my low karma)