Is someone who claims commitment to Islam but steals people's money considered a Muslim, and if so, is it permissible to abandon Islam because of the actions of such individuals?

Ethics are the foundation upon which nations are built, and the Prophetic texts have emphasized their great importance, such as his (peace be upon him) saying: "I was sent only to perfect noble character," and "The best of you in character are the dearest to me and the closest to my assembly on the Day of Resurrection." A Muslim, through his ethics, can be a caller to Islam. As for the person mentioned, he represents himself, not Islam. Your anger should not lead you to seek a religion other than Islam or to say that you are not a Muslim. Deal with him through reconciliation or litigation.