Google Workspace isn't required. Your assistants can also work in a mailbox and a calendar outside Google.
Another mailbox
Any mailbox your provider lets other apps reach over IMAP and SMTP connects: iCloud Mail, Fastmail, Zoho Mail on a paid plan and Gmail do. In the Maxiful app, open the Connections page, find Email and choose How to set up. You enter your provider's IMAP server, your address and an app password made in your provider's account settings, and list the senders you allow.
What it does
Your own assistants read your newest mail when you ask and save replies as drafts. Sending waits for your yes on a card first, unless you let an assistant do that kind of thing without asking in Settings, Approvals.
New mail from the senders you allow can also be read as it arrives, and only when the mail proves who sent it. A restricted assistant reads each such message and puts a summary in your conversation with your Chief of Staff. That assistant cannot send email, move or mark messages, or change anything on your computer.
Another calendar
Any calendar that speaks CalDAV connects too: iCloud, Fastmail, Nextcloud, Zoho and others. On the Connections page, find Calendar and choose How to set up, then enter your provider's CalDAV server, your user name and an app password. Your own assistants read your calendar when you ask, and add, change or delete an event only after your yes.
Using both at once
You're not limited to one. Connect your Google Workspace account and another mailbox, and your assistants keep each separate.