for reference, I am on ui 3.0, unlocked firmware on the n20+, but it didn't work on the prior firmware either.
Samsung only ever had 1 45w charging adapter, and it cost $50. I got it so that I could charge my Note 10+ super fast, but was dissapointed when I found that Samsung discontinued the feature for the Note 20 line. If fast charging works with the 25w charger the phone came with, then it works. The warranty for your device states that you should only charge it with this device.