"i can't agree with you anymore" If you have understood the statement correctly, it means that the speaker no longer agrees with you. It is an unusual statement, in that people with similar viewpoints rarely change.
However, It sounds to me like a common expression " I couldn't agree with you more" which has the reverse meaning. In this statement, the speaker tells you that no matter what might happen, they already agree with you as much as is possible. Couldn't (Could not) implies that there is a condition that will not be met.
"Among “be strict in/about/on sth“ This depends on the subject of your strictness. I am strict with my children. I am strict about the time at which my children come home.
You would never be strict 'in'.
You could be Strict 'on' something in certain conditions. Your child wants to come home later than agreed, and to drink. You can be flexible on the time at which they come home, but you would be strict on the drinking.