See my answer in another thread: Read elements from an array using constant_request_rate - #3 by nedyalko
Your case is similar, though even more tricky. With ramping-vus you can’t know how many iterations each VU will complete, so if it’s a strict requirement to not re-use the same elements out of the array, it’s impossible to use __VU and __ITER to accurately select elements. A per-vu-iterations executor would make this easier as @dan_nm mentioned above.
Something like xk6-counter might be the only way to handle this if ramping-vus and unique data are a requirement.