The future of Windows Workflow Foundation in the context of .Net Core lies with the open-source project CoreWF.
Windows Workflow support in .Net Core
In my previous WF overview blog post – Windows Workflow Foundation in 2017 – I mentioned a very high degree of interest from the community for a .Net Core version of Windows Workflow; despite that, Microsoft didn’t see a strong enough business case and as a result, CoreWF (an unofficial port) was born:

Microsoft re-emphasized earlier this year that .Net Core is the future of .Net and that WF will not be a part of it, forwarding interested parties to the open-source community project.
In order to facilitate the transition to the OSS project, the WF sources (including xamls) were previously added to the reference source:

CoreWF – the future of Workflow Foundation
The Windows Workflow Foundation (full) version that ships with .Net Framework (4x.x) will still be supported in the future – Sharepoint uses it and its end of life is 2026 – however it is most likely that no new features will be added, only bug-fixes will be provided (e.g. see Net 4.8 WF release notes). Started by Dustin Metzgar (former PM of Workflow at Microsoft), CoreWF, the opensource port of Windows Workflow Foundation for .NET Core, is now sponsored by UiPath.
CoreWF is the natural step for those with vested interest in WF, wanting to transition their projects to .Net Core:
- today it offers a working WF runtime + ETW tracking provider + Xaml support (via portable.xaml)
- in its current state, it is not a full replacement for the .Net 4.x WF version (e.g. the Rehosted Workflow Designer is missing), but hopefully in time the project will grow
* Reference Links
a good analysis of WWF LTS in 2021.01 https://blog.inedo.com/dotnet/windows-workflow-foundation