USD Index (USX) / US Dollar is just a number that lets you track performance of the instruments comprising the index, so you can't invest in it directly. But you can buy USD Index (USX) / US Dollar futures or funds or invest in its components.
The lowest ever quote of USD Index (USX) / US Dollar is 89.163 USD. It was reached on Jan 6, 2021.
USD Index (USX) / US Dollar reached its highest quote on Sep 28, 2022 — 114.743 USD.