Does semen smell like yeast, and if so, what is the ruling on my prayer for which I did not perform ghusl due to my ignorance of that?

Jurists explain that the smell of semen resembles the smell of palm spathe or dough. However, the mere presence of a similar smell does not definitively confirm the emission of semen.

Unless you are absolutely certain, with decisive conviction, that semen necessitating ghusl (definition) has been emitted, the default is that it has not. If you are in doubt whether it is semen or vaginal discharge, you have the choice to assign it the ruling you prefer.