Can I add a business email to an existing Apple ID for unified mail access?

I currently have one Apple ID, with have two email accounts. I would like to add a business email via an Apple ID.

can I have two Apple IDs on one computer?

ultimately, I want to be able to see all email accounts (personal and business) by only opening my one mail account.

but those accounts are still separate.

[Re-Titled by Moderator]