Platform not supported error - Newtonsoft

First step first:
. Plastic arrives. Forces me to update “version control” in Package Manager.
What happens after this, is that all Json references start handing out errors, like the new version kicked out the json libraries.

So I have to install a previous asset “JSON .NET for unity” from the asset store.
I import it, all blocking errors go away, as the json references now works.

Testing the game via the Editor works all good, however, when trying to build it and start either a host or a client from thar build, there is an instant error “Platform not supported”. The client cant read any strings using newtonsoft for some reason so nothing works there.

One solution was to update the API Compability Level. Doing so removes any debug feature in the build, and dosent resolve anything. Im at loss on how to handle this.

And why did upgrading the veresion control remove the built in json handler in the first place?

You can fix that. Please consider using proper industrial-grade source control in order to guard and protect your hard-earned work.

Personally I use git (completely outside of Unity) because it is free and there are tons of tutorials out there to help you set it up as well as free places to host your repo (BitBucket, Github, Gitlab, etc.).

You can also push git repositories to other drives: thumb drives, USB drives, network drives, etc., effectively putting a complete copy of the repository there.

As far as configuring Unity to play nice with git, keep this in mind:

https://discussions.unity.com/t/736093/3

Here’s how I use git in one of my games, Jetpack Kurt:

https://discussions.unity.com/t/807568/3

Using fine-grained source control as you work to refine your engineering:

https://discussions.unity.com/t/826718/2

Share/Sharing source code between projects:

https://discussions.unity.com/t/719810/2

Setting up an appropriate .gitignore file for Unity3D:

https://discussions.unity.com/t/834885/5

Generally setting Unity up (includes above .gitignore concepts):

https://thoughtbot.com/blog/how-to-git-with-unity

It is only simple economics that you must expend as much effort into backing it up as you feel the work is worth in the first place.

“Use source control or you will be really sad sooner or later.” - StarManta on the Unity3D forum boards

If instead you want to continue with Plastic, good luck. Here are some general package manager notes since that thing gets itself wedged frequently enough that I keep this list handy:

Extra unwanted packages in new projects (collab, testing, rider and other junk):

https://discussions.unity.com/t/846703/2

About the fastest way I have found to make a project and avoid all this noise is to create the project, then as soon as you see the files appear, FORCE-STOP (hard-kill) Unity (with the Activity Manager or Task Manager), then go hand-edit the Packages/manifest.json file as outlined in the above post, then reopen Unity.

Sometimes the package system gets borked from all this unnecessary churn and requires the package cache to be cleared:

https://stackoverflow.com/questions/53145919/unity3d-package-cache-errors/69779122

Plastic, that very much felt like a forced update (seeing that pop up arrives at every other second) and that it is a commercial product, I dont see why this should be avoided. Actually, I like plastic, it integrates a lot easier with unity.
The main issue here, are why the standard built in jason library disappeared while updating the version control (downgrading made it come back). And why Im getting errors using a common unity asset (newtonsoft) on a build for windows and not in the editor.