How do contacts sync work when you don't use iCloud for email? Pertains to Mac and iPhone and iPad.

I have a MacBook (just switched to Big Sur v11.2.3), iPad and iPhone (both iOS v14.4). I seem to have problem with syncing Contacts across all 3 devices. Initially, after I switched to Big Sur I had duplicates of all my Contacts on my Mac, so following instructions described on Communities I restored my Contacts to what I had prior to switching to Big Sur. However, I still have duplicate Contacts on the Mac after restoring pre-Big Sur Contacts. What I can't tell you is whether I had duplicate Contacts on my Mac before I switched to Big Sur.

I use gmail for my email; I do not use iCloud email. I do use iCloud to sync other things, i.e., Photos, Calendar, and these seem to work fine.

I seem to recall someone telling me that since I don't use iCloud for my email this creates an issue with my Contact Groups.

So, before I start cleaning up all the duplicate Contacts I'm trying to figure out how this all works and which Contact "Group" I should be working with.

For all 3 devices, under settings/accounts, under "Apps using iCloud" it shows that Contacts is turned ON; Mail is turned OFF. (FYI, if I try to turn on Mail it then asks me for my iCloud email, which I don't have.) There are also other apps turned ON such as Photos, Calendar, etc.

For all 3 devices, under Contacts, it shows 2 mail groups: "iCloud" and "MyName". The Mac also show 2 additional groups: "All on my Mac" and "Last Import". Screenshot below shows number of Contacts in each Group

So, questions:

1. My email address is with gmail and I prefer not to switch to an iCloud email address...this would cause major headache with respect to informing people and so for. Also, I'm not sure of the benefit of using iCloud email. Is this a problem?
2. If I don't plan to have my email in iCloud for email, how does Contact syncing work?
3. If I don't plan on using iCloud email, which Contact Group is the one I use? Should I be ignoring the Group "iCloud" and it's sub-groups and just focus on the group "MyName"? If yes, I want to make sure I've set it up correctly, so what do I need to do?