Hi, thank you for the constructive feedback! With "funnelling" level design I assume you're referring to the metroidvania progression? The only few dead ends the entire world map has should lead to rooms with items. Otherwise I've tried to use the design philosophy of games like Metroid Prime 2 for progression, meaning you almost never have to backtrack outside of the immediate area to progress through to the next upgrade, so there should be as little confusion as possible.
But maybe the optional item expansion rooms could be more obviously optional? That's certainly possible, and I thank you for bringing this to my attention so I could take another look at some of the level design and reconsider if the invisible holding hand is gripping tight enough ;)
Also, I will definitely check your game out soon! :)