This is showing up on all 2012R2 Windows servers as being needed, but still is not in BigFix. It’s been a while now since it was released.
2019-12 Security and Quality Rollup for .NET Framework 3.5, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8 for Windows 8.1 and Server 2012 R2 for x64 (KB4533097) Windows 8.1,Windows Server 2012 R2 Updates 12/5/2019 n/a 194.2 MB
Edit: Also, the .NET update for 2008R2 KB4533095 is not in BigFix either, but is in WSUS. I assume there is no plan to make this available in BigFix?