There isn’t an “Edge” replacement for SmartApps so transitioning that app isn’t possible.
Below are pretty much the only options once the Groovy platform is retired and if I created a new app (Option 1) users would have to figure out their own way to host it.
That’s not straightforward and there are bunch of different ways it could be done which would make it difficult to support and at this point it’s not worth the effort…
Once I’ve finished all the drivers on my To Do list I’ll put some more thought into it because maybe’s there’s a simpler solution I haven’t thought of…