What about "tôi yêu vo tôi"?
It's correct and more natural.
This was a word selection exercise for me, and của wasn't even on my list of options.
It's common to omit "của" in this case. So don't worry about "của" not showing up in the word selection exercise.
What were the words in list?
✔ tôi yêu vợ của mình.
X Tôi yêu phở của mình.
So, I can say "vợ tôi", but I can't say "vợ anh ấy" ? (that is, I can omit "của" with "tôi", but not with "anh ấy")
If so, what exactly is the rule for when I can omit "của"?
I don't know if you can't say 'vợ anh ấy' on Duo. But in daily speaking, we often use 'vợ anh ấy', and as a southern speaker, sometime we say 'vợ ảnh' (ảnh stands for anh ấy, not the photo) ;)
Why is it not 'của mình' here?