In short, adjectives always agree with the noun that they modify.
Sometimes, other nouns depend on these adjectives. These nouns are then put in the dative case to indicate that dependence.
locus = noun (“place”)
locus idoneus = adjective agreeing with locus (which place? the suitable place)
locus idoneus templo = noun depending on idoneus (suitable for what? suitable for a temple)
What you are saying is that the adjective will always agree with the
noun that it modifies and then the noun depending on a word like
‘IDONEUS’ is put in the dative.
PRAEMIUM GRATUM PUERIS
Nominative Neuter + Nominative Neuter + Dative
The adjective conjugation of -UM -I -O -UM -O is not important here and
-UM overlaps coincidentally. It is not a question of the dative it is
a Nominative neuter agreement which uses the same ending
What you are saying is that the adjective will always agree with the
noun that it modifies and then the noun depending on a word like
‘IDONEUS’ is put in the dative.
Yes, this is correct.
(Now, some adjectives take nouns in the dative, while other adjectives take nouns in the ablative or genitive. You’ll have to learn the particular case associated with a given adjective as you go along. But most takes nouns in the dative.)
The adjective conjugation of -UM -I -O -UM -O is not important here and
-UM overlaps coincidentally. It is not a question of the dative it is
a Nominative neuter agreement which uses the same ending
is this correct?
Yes, if I understand you correctly. Let’s use a third conjugation noun instead.
Notice that the adjective (grata) agrees with the noun (ars). The second noun, pueris completes the sense of grata by appearing in the dative case. In other words, we answer the question “an art pleasing to whom?” with “to boys”: pueris