Is it forbidden to use the name "Allah, I want none but Him" on Facebook, especially when "Allah writes..." appears to the messenger?

The described case is not an appellation using the names of Allah, but rather an identification of phrases that some people adopt as a slogan or a distinguishing mark on social media, just as scholars and kings used to have seals with religious inscriptions on them. There is no harm in writing it as a personal identifier on social media, especially since it does not show disrespect towards Allah or His attributes. It is advisable to change it to "I want none but Allah" to avoid confusion when only a part of it appears.