Multiple domains on google workplace and email should be added as secondary or alias for email outreach?

We are setting up our outreach management for a new startup.

The app primary email domain is something like app.com

Emails we send out will be via a new domain, something like app-email.com.

We use google workplace, adding another domain is ok but we can either do so as a secondary or alias domain. An alias is best for our end as all emails will be in 1 inbox.. but this might not be the best overall.

The reason we are advised to setup a 2nd domain is for mitigating the risk of being blacklisted during an outreach campaign. Should the email address's domain get marked as spam (then we are doing emails very wrong we know) then at least our app's primary domain is safe.

This practice can be seen from many providers, even apple do this.

My question is:

The 2nd domain can added as an alias or a secondary email in google, but is an alias safe or will our primary domain still be at risk of being pulled onto a blacklist through the alias relation?

Or

Is it possible to even send an email from an alias email?