Is a text from an Ohio lanlord legal notification of no refund of deposit?

Yes, I would think so, because it's 'written.'
The rest depends on why the deposit was not refunded. There are laws governing explanations and proof.

Not unless the text included an accounting of how the deposit was used. If they are past the deadline I'd go to court over it.

Does it detail the deductions? You can dispute any damages you don't agree with bit you would have to prove it.