Jarte is indeed out of support as far as ongoing development and maintenance, but given the nature of the program, and that the producers are still keeping their website active and allowing downloading of Jarte Plus at no cost, they're not telegraphing that it should not be used.  It lives in a sort of twilight world where its makers are not pulling it but they're also not doing any further development on it.  It's not unlike Classic Shell in that regard, although the makers of CS are pointing people to Open Shell, if memory serves.

Should there come a point where something actually breaks as far as Jarte and Windows 10 go, then the only alternative would be another alternative.  That's just the way it goes with abandonware, as it's often called.

Since Jarte does not, if memory serves, have much (if any) intimate contact with cyberspace outside its update function which, obviously, will no longer work I would not feel uncomfortable using it from a security standpoint unless something is found with regard to it having a previously undetected vulnerability to attack.
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Brian - Windows 10, 64-Bit, Version 21H1, Build 19043  

I do not understand why some seek to separate a person from their actions.  The self is composed of an individual’s thoughts, actions, and expression, which are contained in and actuated by the body.  What you do and say is the clearest indicator of who you are.

      ~ Brian Vogel