Did you measure it? I would expect using % would ruin your performance as it's slow, even if it allows you to avoid doing a bunch of sums (which are fast).
Note that the conversion of numbers to base 10 to check the digits typically involves doing division and modulus operations, so you are already doing those even if you remove the modulus operation from this check. That is unless you find a clever way of extracting the digits using the modular multiplicative inverse to calculate x/10^k.
https://extendedeuclideanalgorithm.com/calculator.php?mode=2...
For that matter, the naive "convert to string and convert each digit to int" approach becomes faster in pure Python than using explicit div/mod arithmetic for very large numbers. This is in part thanks to algorithmic improvements implemented at least partially in Python (https://github.com/python/cpython/blob/main/Lib/_pylong.py#L...). But I can also see improved performance even for only a couple hundred digits (i.e. less than DIGLIM for the recursion) which I think comes from being able to do the div/mod loop in C (although my initial idea about the details doesn't make much sense if I keep thinking about it).
Also, you don't have to use % in order to decide whether to perform the sum-of-digits check for a given value. You can just iterate over values to check in steps of 9.