You can now install One UI 4 on the Galaxy Note 20 and Galaxy Note 20 Ultra. However, you must have bought your device in the UK to be eligible to receive beta builds. Likewise, One UI 4 is also available on the Galaxy S20 series in the US.
https://www.notebookcheck.net/Samsung-opens-One-UI-4-beta-programme-to-the-Galaxy-Note-20-and-Galaxy-Note-20-Ultra.578152.0.html