Apple Mail with multiple Internet Accounts MBP-M2 and iPhone13

I am new to the Apple verse and am coming over from 15+yrs of Windows and Android and I'm having a bit of difficulty with Apple Mail app.

Here is my setup:

Macbook Pro M2 - 2TB - 32gb mem. macOS v. Sequoia 15.0.1 (24A348)

iPhone 13 iOS 18.1 (22B83)

iCloud+ Subscription (2TB - 200gb used so far) MBP>System Settings>MyNAME>iCloud>Mail>iCloud Mail>Sync this Mac (turned on / green)

OK, here is my scenario. I have about 9 Gmail accounts, 4 Outlook/Hotmail accounts & 4 Yahoo accounts. I'd like to get all the mail (only mail) to Apple Mail for a 'single pain of glass' viewing, editing, writing setup.

My current setup:

*Macbook Pro Mail I setup two additional accounts (PRIME-icloud.com, A-Yahoo & A-Gmail) - I added these accounts 'System Settings>Internet Accounts>Add Account

*iPhone 13 Mail I setup two additional accounts (PRIME-iCloud.com, B-Outlook.com & B-Gmail) Added directly on iPhone 13 Settings>Apps>Contacts>Contacts Accounts

Issues:

My non iCloud mail Mailboxes do not sync across devices... The accounts I setup on my MBP do not show up on iPhone and the accounts I setup on iPhone do not show up on MBP. I've gone through numerous restarts and connected iphone directly to MBP but without success. (PRIME-icloud.com mailbox is fine on both devices)

Is Apple Mail app not conducive to what I am trying to achieve with my 'Single Pain of Glass' management setup? Currently I have all the different mail apps on iPhone and browser for MBP to view and manage my email but I was really hoping to consolidate to one platform/app.

Any ideas on how to further troubleshoot - anyone else with a similar workflow with a lot of non-Apple email accounts in Apple Mail?