Package metadata has been fixed on the backend. This will apply to all editors performing a search (hence no Unity changeset to provide for the fix).
com.unity.xr.oculus v3.0.0-pre.2 now has metadata "unity: 2021.2" and "unityRelease: 0b17" meaning it will only be discoverable from 2021.2.0b17 onwards.
com.unity.xr.oculus v2.0.0-preview.2 now has "unity: 2020.3" and "unityRelease: 21f1" meaning it will only be discoverable from 2020.3.21f1 onwards.
Verified fix with repro project in 2019.4.39f1 - versions 3.0.0-pre.2 and 2.0.0-preview.2 do not appear in version list.
In 2020.3.35f1, v2.0.0-preview.2 does appear as expected. v3.0.0-pre.2 does not appear.