Hello @Flavia , in order to make your Azure AD Dynamic Group matches users whose account are enabled and one of other or expressions you need to enclose the or expressions in parentheses. Eg:
(user.accountEnabled -eq True) and ((user.extensionAttribute1 -contains "E") or (user.extensionAttribute1 -contains "C"))
Let us know if you need additional assistance. If the answer was helpful, please accept it and rate it so that others facing a similar issue can easily find a solution.