a) figure out how to make the "messy and dangerous" doable.

b) I had some success by playing boardgames (even Carcasone) at this age, with some rules-simplifications

c) sometimes we played games on my phone, Monument Valley, I love Hue, Chuchel ...

d) Buying and launching a model rocket was a success, if he'd enjoy watching from the distance and then trying to find the rocket again :-)

e) in simmilar fashion, building a kite (or buying ... tbh I usually do both, because building is fun, but the store-bought actually works :P ) ... but you need good wind-conditions to fly it

f) museums are surprisingly good these days, especially modern technical museums can often entertain both 3yo and 30+yo