It will not hurt anything to not push hand dominance at this time. Just always work with his hand of choice. This might change from day to day or even activity to activity but always let him pick. My son is 5 and he still doesn't have a hand dominance. He has beautiful handwriting and has above average cutting skills. So go with his lead he will pick a hand when ready but in the meantime you can work the skills with both hands.

My son did the same... did not show a hand preference at age 3 but we wanted to do fine motor things. So we decided to pick the right hand since there's more things built for right-handed people.

My son is now 18 and that worked out well.

Our son almost 6 is the same. I just try to help him with whatever hand he chooses. I'm ambidextrous, and I thought it couldn't hurt him to develop motor skills with both hands.

My son is almost 10 years old and still uses both hands for various activities. He does use his right hand for writing.

There is some research on this mixed hand topic (more about prevalence which is as reported as 30% and as high as 47% in one study) as well as theories based on neuroscience, but nothing practical to advise. With our older NT son, it was obvious even at 1 year old (right hand dominant), but for our ASD son, it is 50/50 for most things including while using iPad.