Row / Column tweak logic:

Comparison: L ^ 0.5 <= row <= col <= L ^ 0.5

In the case where L is not a perfect square num, you would increase col by 1
After incresement, if row x col is smaller than L, just increase row by 1 as well.
Then you should get row, col pair based on challenge's rules.

zip_longest():

from itertools import zip_longest

# Use it to combine 2 iterables:

wordlist = ['apple', 'grape', 'rank']
print(*zip_longest(*wordlist, fillvalue = '_'))
# Output: ('a', 'g', 'r') ('p', 'r', 'a') ('p', 'a', 'n') ('l', 'p', 'k') ('e', 'e', '_')

import math
from itertools import zip_longest

def encryption(s):
    # Write your code here
    # Remove spaces and calculate the length
    new_s = "".join(s.split(" "))
    l = len(new_s)
    row = col = int(math.sqrt(l))
    
    if not math.sqrt(l).is_integer():            
        col = row + 1
        if row * col < l:
            row = col
    
    grid = [new_s[i: i + col] for i in range(0, len(new_s), col)]
    new_grid = zip_longest(*grid, fillvalue="")
    encrypted = " ".join("".join(items) for items in new_grid)

    return encrypted