Tania.......One questione......of i use gmail and no stock email Is It Better e ti deactivate stock app or not?also scanner etccccc
One thing is using GMail account (you need for Google Playstore, YouTube app,Find My Device, etc) and the other is to use or not GMail app
You may not use your Gmail address for mail communication, or you may read/write with your gmails via browser. Or you may download and use 3rd party mailing apps like Blue Mail (and use it for also instead of Outlook for your Office365 mail account and other mail accounts)
It's all about your preferences. Like which browser would you use, Chrome, Edge, Firefox or who knows. Or like blue or red sofa in the room - it's not like, what is better
Mi account - up to you, do you want to use their cloud for backups and their protection (in case the phone is stolen a thief cannot unlock if you had properly set pin/fingerprint, hence a thief may attempt to factory reset or flash a ROM, but MIUI would not allow to activate the ROM without a password from the previously configured MI account on the phone - some have troubles with if they forgot their Mi account password in the meantime)
Eg, I use two Gmail accounts (both for communication but I can also switch which of them to use in Playstore, YouTube, Chrome, etc). And I always use Mi account on MIUI ROMs. But I always uninstall (if possible, or disable or debloat) Gmail, stock Email or other mail apps and install the ones I prefer (traditionally Blue Mail for gmail and my private mail addresses - but nowadays there might be other and better clients, and Outlook for my office account)