Hi,
Yes, you need a implementation plan to carry out this migration as it involves lots of components form infra to application.
Again, the authentication factor in Azure AD also have options like pass though / password hash sync etc when you moving away from ADFS.
Major factor to consider is your application support for Azure AD based authentication.
Start with the below articles to get an understanding on the migration approach.:
https://learn.microsoft.com/en-us/azure/active-directory/manage-apps/migrate-adfs-apps-to-azure
https://techcommunity.microsoft.com/t5/core-infrastructure-and-security/ad-fs-to-azure-ad-migrations-notes-from-the-field/ba-p/2635847
Migrating all your application authentication to Azure AD is optimal, as it gives you a single control plane for identity and access management.