The functionality for the UNIQUE formula was to be added to CALC in 24.8. I attempted to use the formula in 24.8 AlPHA, and it appears to be missing. It did not present itself.
That's because it was added after alpha1. See bug 126573 comment 27. Grab a daily build from https://dev-builds.libreoffice.org/daily/master/current.html or wait for beta1.
I do appreciate the update on the bug. Not sure if I should submit another ticket, but think I found one from the my loaded current build. If you enter =yearac(As,B2)*12, one should get the time between dates such as, 12 Jan, 2020 and the next cell is 20 June, 2020. That formula should return a number of 5.27. When entered on LibreOffice, I receive a value error.
Doesn't sound like it involves UNIQUE, so please create a new report.