Magnetic Flux is learned by 8 species by level

Effect, in PokéAPI's words

“Raises the Defense and Special Defense of all friendly Pokémon with Plus or Minus by one stage.”

Who learns it

8 species in all, 7 games

Scarlet and Violet: 7 species

Species	Method	Level
Electrode	Level up	1
Ampharos	Level up	1
Magnezone	Level up	1
Probopass	Level up	1
Magearna	Level up	24
Zapdos	Level up	65
Sandy Shocks	Level up	91

Brilliant Diamond and Shining Pearl: 5 species

Species	Method	Level
Electrode	Level up	1
Ampharos	Level up	1
Magnezone	Level up	1
Probopass	Level up	1
Zapdos	Level up	65

Sword and Shield: 3 species

Species	Method	Level
Magnezone	Level up	1
Klinklang	Level up	1
Zapdos	Level up	65

Ultra Sun and Ultra Moon: 6 species

Species	Method	Level
Klinklang	Level up	Evolve, 1
Electrode	Level up	1
Ampharos	Level up	1
Magnezone	Level up	1
Probopass	Level up	1
Zapdos	Level up	92

Sun and Moon: 6 species

Species	Method	Level
Klinklang	Level up	Evolve, 1
Electrode	Level up	1
Ampharos	Level up	1
Magnezone	Level up	1
Probopass	Level up	1
Zapdos	Level up	92

Omega Ruby and Alpha Sapphire: 4 species

Species	Method	Level
Electrode	Level up	1
Ampharos	Level up	1
Magnezone	Level up	1
Klinklang	Level up	1, 76

X and Y: 4 species

Species	Method	Level
Electrode	Level up	1
Ampharos	Level up	1
Magnezone	Level up	1
Klinklang	Level up	1, 76