How to save a photo into IOS Photos for Mac?

Q: How do I automatically acquire photos downloaded from an email, into my IOS photos on my MBP?

BACKGROUND:

Long time IOS user, but this constantly frustrates me. I use gmail, and if someone shares a photo with me via email, I want to download it into my IOS Photos.

I click on the photo, title it, click Save -- and it's in Downloads but NOT in my Photos.

What am I doing wrong??

I want to have these photos available to share elsewhere, just as usual.

Yes, I already restarted my laptop.

Yes, it's all up to date.

Yes, I already completely closed and reopened the Photos app.