Learn Turkish: Toplantıya katılım zorunlu olmayacak. - Participation in the meeting will not be mandatory.

It comes from the verb katılmak (to join or participate). By taking the verb stem katıl- and adding the derivation suffix -ım, we create the abstract noun katılım, which means participation or attendance.

Could we use katılmak or katılma instead of katılım in this sentence?

You could say Toplantıya katılmak zorunlu olmayacak (To participate in the meeting will not be mandatory). However, katılım acts as a pure noun, making the statement sound slightly more formal and institutional, much like using participation instead of participating in English.

Why is Toplantıya in the dative case if katılım is a noun and not a verb?

Abstract nouns derived from verbs often keep the case-marking rules of their root. Since the verb katılmak requires the dative case to show what you are joining, its derived noun katılım also takes a dative object for the event being attended.

How is the word zorunlu (mandatory) built, and is it related to zor (difficult)?

Yes, it comes from the noun zorun (obligation or necessity), which is built from the root zor. Adding the suffix -lu, which means having or containing, gives us zorunlu, meaning mandatory or compulsory.