Forget about non admins, I'm a mail admin and your post is still a bit confusing to me but I understand the big picture. No offense but I highly doubt non mail admin can understand the post.
>> They have done things to my domain DNS record that have been ineffective and/or that I learned subsequently breaks DNS - eg entering multiple SPF records. I have escalated to management on 2 occasions but been told it will go away by itself, or been told its a google problem.
The problem is editing a DNS record actually adds a new entry but it does not delete the old entry. That's how you end up with 2 SPF records. Edit normally adds a new one and automatically deletes the old one. Many GoDaddy customers have multiple SPF records problem. It makes it invalid and resulting in their email getting rejected.
>> Why this wasn't done when Microsoft 365 on GoDaddy was set up, I don't know.
I don't know how you get your mail hosting service, I did everything myself. That includes setting up SPF, DMARC and DKIM records correctly since the beginning of my subscription. I suspect GoDaddy didn't take care of it because it wasn't mandatory in the past or they expect customers do that on their own.
Most users who experience this problem are just mail users. They post problem here and wait/expect someone will fix it someday. They don't realize they are the only ones who can fix the problem.
I have been following a few similar discussion threads. I have told them the problem and what needs to be fixed. Occasionally I check back to see if they fix their DNS records. Nope. They're still missing or have invalid records. That tells me they don't understand my replies.