Navigating the recitation in Salah: seeking clarity on the final rak'ah

As-salamu alaikum everyone, My dear mother taught me how to perform Salah. I remember her instruction that after reciting Al-Fatiha in the third rak'ah, you don't say another surah, and then in the fourth rak'ah, you do. This has been my practice for over two years. But recently, I came across information that reciting another surah in the fourth rak'ah isn't the right way to do it. Now I'm feeling a bit lost-what should I follow? Has anyone else prayed this way or have insights on this? I plan to talk to my mother about it, inshaAllah. JazakAllah khair for any advice you can share!