I think the question shouldn't be "experience or thing" but rather "what combines the best of both". Because the drama of choosing just one is that you end up regretting it, you know? If you give only the experience, boom, it's over and all that's left are photos. If you give only an object, it might end up being something they don't use or that gets forgotten in a drawer. What really works after 5 years together is putting both things into the equation somehow, even if it's in a creative way.
What nobody mentions is the risk that the experience turns out to be a flop because there are factors outside your control (weather, crowds, the place being closed that day, the other person not being in the mood). A nice trip can turn into a logistical disaster and then your gift backfires. An object, even if it's more "simple", guarantees it'll at least exist forever. But you shouldn't get obsessed with tangible stuff either, obviously.
My suggestion: why not a physical gift that has to do with an experience or that creates one? A nice space to live something together, something they'll use in the future to do things. Or give the experience but pair it with something small that represents it (a souvenir from the place, something related to it). What matters is that after 5 years your partner feels like what you gave them is for you two, not just a "checkmark" on your anniversary 😊