MightyZehir
Explorer
Abilities without keywords should work in antimagic field.
Check out the demilich.
All of the demiliches main abilities lack keywords such as "spell", "casting", "magic".
Their lair actions includes creating an antimagic field.
Clearly that is meant to be to the advantage of the demilich, together with their immunity to nonmagical weapons.
It would always be up to the DMs to decide since magic effects are not clearly defined in 5E.
I use these keywords to make my rulings fast and consistent.
As for the demilich, I would rule that its howl and life drain still work in anti-magic field while its legendary actions except flight would not function.