Can be challenging to find the pattern, but really easy to solve once the pattern is found. Will post the first column if hints are needed, as that's all that is required to solve the rest of the puzzle. Thank you for the puzzle.

Very easy. Thanks.

Start with R1 C2-3. Find other rows with the same sequence as R1 and fill in C2-3 in those rows too. The pattern should soon become apparent.

Well did it bit tedious but looks nice especially in the small square.