Enthusiasm for the Betas never fails to impress me! I've merged a few threads together... and edited out some links lol. We don't recommend that folks download software from a non-official Samsung source as that can open you up to security vulnerabilities. (Or, in other words, along with the goodies you're after you might get a nasty surprise from some ne'er do well. 😉)
Now that the One UI 3 Beta is officially open for UK S20 open-network users, I'll close this thread off so that folks can share their Beta-related stuff in the announcement thread here: https://eu.community.samsung.com/t5/galaxy-s20-fe-galaxy-s20-galaxy/uk-oneui-3-beta-programme-s20/m-...
I believe once the programme is ready it'll be shown in the Samsung Members App where a person can then register their interest to apply to be a Beta Tester @Moyah8
Current Phone ~
Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+
Samsung One Ui 3.1/ Android 11.
As @BandOfBrothers said. Once it's out as public beta. It should show up in Samsung Members app to register. Right now, It's in pre-beta for developers. Pre-beta is now closed for applications.