It's not a Gmail thing:

> The reason why my IP address is visible is because Apple Mail sends emails with SMTP.

Unless you use a proxy, your IP address is visible to an SMTP server, just like it's visible to an HTTP server when you use a web browser. This is not specific to Apple Mail or to Gmail.

Yeah but I think Gmail seems to actually just keep that header rather than nuking it. To be fair I don't entirely know what I would do to fix it since (like the post) this seems like there aren't many good options here.

Gmail's SMTP servers are what's adding the received header with your IP address, not Apple Mail.

> I think Gmail seems to actually just keep that header rather than nuking it.

I think that's common among email providers.

Yes, was able to repro just now

I clearly remember many years ago that this wasn’t the case with Gmail, when looking for the source IP address in a case involving harassment of a person. I could only get Gmail’s own IP address in the headers from the multiple emails I examined at that time.

Nevertheless, as js2 said in another comment, it’s your mail provider (in this case Gmail) deciding whether to include the sender’s IP address or not.