Honestly you should slow it down a bit then.
Take a min to read more about the process. It is so easy when you know more what to do. Obviously its easier from practice so good to keep trying.
But yeah all you need to do is:
Install twrp from fastboot
Install a ROM
Install gapps
Format data (emphasis on format when you come from MIUI)
Boot
Boot back to TWRP recovery and install magisk
Done
Twrp:
https://github.com/xiaomi-msm8998/twrp_device_xiaomi_sagit/releases/tag/3.2.3
Magisk: 18.1 from official thread
Shameless self-promo:
You can use this video for some reference. Coming from MIUI you DONT want to use migrate and you DO want to format data
https://m.youtube.com/watch?v=oRSIqV05bEA
(Don't worry if you can't hear me I know the music is too loud. The process is all visual anyway. Applies to all pie ROMs)