I would probably do this, this is not an array formula

=INDEX(A1:F1,1,MATCH(FALSE,INDEX(A1:F1="",,),0))

how it works if you interested

index(A1:F1="",,) creates a true or false value for each cell in that range based on if its empty (true) or contains info (false)

match(false(above statement),0) returns the first value where the false statement occurs (value = 5 in this case)

index(A1:F1,1,5 (from above) = plain old index returns the value of that cell

I find an explanation also helps you to discover your own way to solve these issues.