Having Azure AD does not prevent clients from also having Okta or any other 2FA provider for 2 factor authentication. In fact, I have worked with at least 10 clients in the last 2 years that used Azure AD for authentication but then something else for 2-factor depending on the type of apps.
Sometimes even within one company, there are multiple 2FA protocols, e.g. using Oracle single sign on for ERP apps but Okta for Citrix and other external facing apps.
Sometimes even within one company, there are multiple 2FA protocols, e.g. using Oracle single sign on for ERP apps but Okta for Citrix and other external facing apps.