Use WWF - Windows Workflow Foundation or Similar Workflow tools in current latest .NET CORE application?

You can call any API you want in WWF. It doesn't matter what the server on the API backend is implemented in. It has no bearing on the ability to call it. Think about popular APIs you might be using today such as Twitter, Facebook, Azure, AWS, etc. Who knows what language(s) they are written in. Provided you can call an HTTP (REST) API then the API server language isn't relevant. For .NET the class you need to call an HTTP API is HttpClient and that type is available in all framework versions, albeit with a few differences depending on your framework you are running on.

More importantly VS can auto-generate the necessary code if the API implements OpenAPI. You can access that by going to Connected Services in your project node of Solution Explorer.

But using WWF is not recommended, unless you already have a working solution. WWF is getting left behind in a NET Core world. If you're still using NET Framework then it is still available but you won't be able to migrate that code to NET Core when you're ready as it doesn't support WWF. MS hasn't really mentioned they are deprecating it that I'm aware of but it isn't getting any attention, it isn't installed by default with VS and there is no Core equivalent. There is a third party Github project to port it to NET Core so use at your own risk.

these is no plan to port windows workflow to .net core. there is an open source port, but is not supported by Microsoft.

a Microsoft supported product would be an azure product, like durable functions or azure logic apps.