Can a lay catholic be elected Pope? Yes, but…
In theory, the primary condition for being elected Pope is to be a baptized and confirmed Catholic man. However the problem is that with recent practices it is highly unlikely for someone other than a Cardinal to be elected since they keep the choices limited to a few eligible cardinals these days.
If a lay catholic was ever elected Pope, he is to be ordained Bishop first before being inaugurated, since a Pope must first be a bishop.