wpllc

Nope, no automatic filter set. See screenshot here: https://ibb.co/Pr7G9Tj

I am already currently using an alias. That alias is actually a Google Group email address. Could that be related to the problem with it auto-archiving emails?

For example:
Google Group Email: support@mydomain.com
G Suite Account Email: john@mydomain.com

WP Mail SMTP is configured to use the Gmail Mailer and is authenticated using the API using the ‘john@mydomain.com’ account.

john@mydomain.com is setup in Gmail to use support@mydomain.com as an alias. It is also configured to always use that alias as the From address.

WP Mail SMTP is also configured to force using support@ as the From address. Which would be fine for the most part, except in the case of the Contact Us form we have.
When john@ receives an email to the group hello@, it shows the name of the person on the form in the From address, but it shows it coming from hello@. If john@ attempts to reply to this original email, the reply-to address is correctly the one submitted with the form, which is fine. However, if john@ forwards the email to someone else to handle, the reply-to address is lost and confusing for some.