When can a magical effect be targeted with the dispel magic spell?

Inspired by the following:

  • Can Dispel Magic be used on a specific magical effect without removing other spells?

The dispel magic spell states:

Choose one creature, object, or magical effect within range. Any spell of 3rd level or lower on the target ends. For each spell of 4th level or higher on the target, make an ability check using your spellcasting ability. The DC equals 10 + the spell’s level. On a successful check, the spell ends. […]

The question for me is what sorts of magical effects can be targeted, we already have (at least) two somewhat related questions:

  • What happens when you target a "magical effect" with Dispel Magic?
  • Can you Dispel a spell buff on a Rakshasa?

The first is just a general explanation that dispel magic ends spells that cause magical effects by targeting their magical effect. It does not address what magical effects you can target, but instead addresses what happens if you’ve already targeted an effect. The latter question asks specifically about the haste spell and has an answer stating:

[…] TheĀ hasteĀ spell isn’t creating a magical effect in the space (that is things like illusions, walls of fire, etc.). If you would like to argue otherwise you are very quickly into the realm of things 5e doesn’t define properly (ie. what is an object, magical effect, etc.?). […]

My question is basically whether or not this is true. Does the haste spell create a targetable magical effect? Are there rules that help answer the question "Does X create a magical effect that can be targeted with dispel magic?"

How do I know if I can target an effect with dispel magic?