Eliminate brush strokes while using Polyurethane?

Use a foam brush

Polyurethane comes in a spray can option! No brush strokes period! Just do not hold over one spot for too long. If not that, then maybe try a foam roller? I just use a regular paint brush for my polyurethane and I never have brush stroke issues. Try sanding with 220 grit or higher in between coats and after the final coat. That should help as well!

I have been told to sand between each coat of polyurethane to lightly sand with a fine sand paper.

What I do now is put a little polyurethane on a damp cloth and then wipe across the item. It doesn't leave brush strokes this way. So if you are afraid of sanding, maybe try adding a few extra layers with the damp cloth and it might level out the strokes.

Try using a foam brush