The spell Compulsion says
Creatures of your choice that you can see within range and that can hear you must make a Wisdom saving throw. <...> On a failed save, a target is affected by this spell
Does this mean that the spell can affect as many creatures as the caster desires, provided that they are within range and the caster can see them, and the targets can hear the caster?
Correct, you can target as many creatures as satisfy the conditions. For reference, the relevant rules on spell targets are:
A typical spell requires you to pick one or more targets to be affected by the spell’s magic. A spell’s description tells you whether the spell targets creatures, objects, or a point of origin for an area of effect (described below).
The spell's description tells us that targets are
Creatures of your choice that you can see within range and that can hear you [...]
The range of Compulsion is 30 feet, so you can target as many creatures as there are within 30 feet of you, provided that you can see them and they can hear you.
