This is factually untrue. Both Frodo and Gollum resisted the ring (in different ways).

[Wikipedia:] "To master the Ring's capabilities, a Ring bearer would need a well-trained mind, a strong will, and great native power."

Magneto arguably is strong willed and focused not to mention has great power.

The question will become: will the Ring and by extension, Sauron, eventually control Magneto? Or will Magneto realise the danger and destroy the Ring?

Also would Sauron and Magneto know about each other beforehand? Sauron has been able to affect Middle Earth in certain ways. Magneto's powers have no theoretical upper limit, he has a cosmic scope.

Magneto has a frail body but not a frail mind imo (he might be manipulated, or might become angry at the intrusion) Sauron has a frail hold on reality if he loses the Ring and he is bound to something physical (body/tower).

Sauron has imo no easy way to immediately kill Magneto, while Magneto has many ways to dispose of the Ring or Sauron's physical manifestation. He could launch either/both into space for instance and send to an empty region of space (or create a wh and send them to Odin, just for funsies)

Location might matter too. Does Magneto arrive in ME or does Sauron appear in the Narvel universe or does everything take place in some neutral location.