That is not correct. You need 218 votes to become speaker. Pelosi will not get 218 votes. She would need 100% of Ds and a few Rs to vote for her.
What could happen is the Ds could whip all of the Ds to vote for Liz Cheney or another never Trumper and a few of the Rs might also vote for them.
"NOT" is a very strong word here.
You seem to think a scenario where all Democrats would vote for Liz Cheney is more likely than a scenario where a few Republicans would vote for Nancy Pelosi. I wouldn't be so sure of that.