“…In quite recent times, many researchers have given the existence, uniqueness, and various structures of Ulam stability and Mittag–Leffler–Ulam stability of solutions for differential equations of fractional order as in previous research [
10–23] and the references therein. In recent years, many researchers have exposed the attention in the field of theory of nonlinear fractional differential equations, which will be used to describe the phenomena of the present day problems; for example, see earlier studies [
24–34]. In this regard, a very significant nonlinear differential equation is the Duffing equation [35]
…”