There are some classes, like the vengeance paladin's capstone or the Tempest Cleric's 17th level Stormborn feature, that grant a flying speed to a creature.
Is this considered 'magical' flight or is it mundane flight?
I'm thinking of this with regard to the rules on falling when a creature has their speed reduced to 0 or if knocked prone:
If a flying creature is knocked prone, has its speed reduced to 0, or is otherwise deprived of the ability to move, the creature falls, unless it has the ability to hover or it is being held aloft by magic
Best Answer
It will depend on the feature itself.
The Sage Advice Compendium clarifies what is meant when a rule references magical. This question tackles that topic in depth, but in short, an effect is only magical if the rules say they are. Otherwise they are simply a mundane part of the D&D world (however magical they would seem in our world).
As for the specific examples you gave...
Neither the Tempest Cleric's Stormborn, nor the the Vengeance Paladin's Avenging Angel count as magical for this purpose. This is because they do not satisfy any of the following conditions:
Contrast this to the Storm Sorcery Sorcerer's Wind Soul feature which says:
Since this flying speed is explicitly called out as magical, it would hold you aloft even if you are knocked prone, or your speed is reduced.