30 reps is definitely too light for optimal muscle growth.

For smaller muscle group like bicep 12-15 is good.

If there is no heavier dumbbells then you make do with what you have.

Muscle will definitely grow but just slower.

Also make sure you eat enough so that there is calorie surplus if you want to gain muscle.

Maybe you should try doing the same reps for both arms so that no muscle imbalance in the long term.