First,
Any questions about compilers are best asked in the Development forums where development is a bit more “hard core” compared to this Applications forum which is more for Users (who may still need to compile something from time to time).
In those forums,
You’ll find questions about Fortran compilers asked a few times in recent years,
There is a single openSUSE package now that provides several of the most used Fortran compilers (following upstream convention, this isn’t anything special to openSUSE).
You’ll likely find what you want in the first listed at the following link the others are just FYI