Firebase Dynamic Links is deprecated, but still supported. From the FAQ on its deprecation and upcoming sunset:

I need to onboard onto Firebase Dynamic Links to enable email link auth in Firebase Authentication. What should I do?

It currently is not possible to newly onboard onto Firebase Dynamic Links if your Firebase project doesn't already have FDL enabled as of the sunset announcement date on August 25th, 2023.

If you need to enable Firebase Dynamic Links to enable email link authentication, please contact Firebase Support and we'll reach back to you to help get you configured.

Note that this continuation of functionality is separate from using Firebase Dynamic Links for the primary use cases of store and web routing, deferred and regular deep-linking, which will be deprecated according to the migration timeline shared above.

So you should reach out to Firebase support to get their help enabling Firebase Dynamic Links on your project for the purpose of using it in email link authentication.