Alternative to authorization code flow with PKCE for native mobile apps that provides native experience

I've been searching for the most advisable standard/protocol for native mobile app authentication, and most of the articles/videos till these days suggest to use authorization code flow with PKCE and stating its advantages.

However, most of my clients (especially who don't need third party login and only has username/pass or phone auth in the mobile app), refuses to have a browser screen popping up for authentication saying that it's bad user experience (and on contrary to what many articles suggest, it doesn't give them relief when they see a browser with URL that this is secure but rather gives them suspension). There was an old question on SO which no longer holds and actually still just trying to work around without providing native experience:
https://stackoverflow.com/questions/58861305/mobile-native-authentication-user-experience-and-alternatives-to-auth-code-pk

so my question is, what is a good standard/protocol that is advised from security-perspective and has good support (available implementations/libs/tools), but still can provide native mobile experience without browsers at all?

In my case (I use Laravel Passport) and although it is no longer a recommended practice, I use the password grant type and the refresh token grant type, I keep the client id and client secret in the backend, from the frontend I only receive the user and password, in the backend I make a request to the authorization endpoint adding the grant type, client id and client secret to the request, so I can provide the frontend with the access token and the refresh token.