I had a large limb ripped from my Magnolia grandiflora in hurricane Milton.
Will the tree survive such injury? Do I need to use a sealer?
Damage diameter is approximately 12" and 4" deep.

Don't use a sealer...

I think I'd cross fingers and hope for the best... trees have been surviving injuries like that ever since there were trees...
I suspect the tree will recover, but will have that big scar for the rest of it's life.

I also feel that you tree will recover; sealers do not help.

I will guess that leaves a weak spot, but cross my fingers the tree stays strong.

Thanks for the feedback and I will not use a sealer.