Does expiation become obligatory for one who vowed to abandon the internet except for what pleases Allah?

Avoiding that which displeases Allah is an obligation according to Sharia. A vow to do an obligation is not valid and does not take effect because it is tahsil hasil (accomplishing what is already accomplished). Therefore, committing to something that is already obligatory is not valid. The view of the majority of scholars is that a vow to do an obligation is not valid, and this is the fatwa given. Some scholars hold the view that a vow to do an obligation is valid, and if one breaks it, there is an expiation for breaking an oath, which is feeding ten poor people, or clothing them, or freeing a slave. If one cannot find these, then fasting for three days.