Is there any way to send transaction emails (I.e invoice) from a domain other than system.netsuite.com? I see settings to change campaign emails to come from my servers but can’t find anything for transaction emails.

Set DkIM

Short answer - no. Longer answer - with DKIM setup it can "appear" as though it comes from your Domain. Also - if you do that, don't forget to set up even a simple DMARC record on your email server as well (refer to suite answers- "Email Best Practices")