The change you’re seeing, with the Storefront API tokens no longer available via the Store’s Admin for custom apps, is expected behaviour.
Moving forward all apps are created in the Dev Dashboard, including both Partner Custom and Public apps, and Merchant Custom apps.
For custom apps, you no longer get both the Admin or Storefront access tokens directly from the dashboard/admin, you will need to use one of the existing authorization methods instead.
For custom apps to get an Admin API token, we recommend using the Client Credential Grant workflow as it is the simplest to use. You will need to take the Client ID and the Client Secret that are listed in the Dev Dashboard, and pass them as a URL parameter in an HTTP Request to POST https://{shop}.myshopify.com/admin/oauth/access_token, and Shopify will reply with the access token that you can use for the Admin API requests.
Here is some documentation that explains this further:
And here is a Shopify.dev Community Forum thread with a bit more info as well:
As for the Storefront API token, what @Dylan mentioned is correct. As long as your custom app has an Admin API token, and any of the unauthenticated... access scopes, you can use the storefrontAccessTokenCreate mutation on the Admin API to retrieve Storefront API tokens.
And more information about Public and Private Storefront API Access Tokens here as well: