Portuguese-speaking countries have made attempts at reconciling their various differing orthographies over the years. This has resulted in spelling changes in the various countries who were parties to the agreement.
I believe it was the Portuguese Language Orthographic Agreement of 1990 that called for the change from «lêem» to «leem». The pronunciation remains the same (NB: I'm not a native speaker).
Obviously quite a few other similar spelling changes exist and are still being used by people who went to school under the older orthographical standards. Many of my textbooks and references also use the older orthography on occasion. Don't let this discourage you. In my experience using the older orthography is not really considered a serious error, nor will you be misunderstood.
As user Ker writes in the first cited link below, you can report instances where older orthography is being used on duoLingo since it is apparently the policy of the course maintainers to use only the newer orthography.
Here are some links for further amusement: