SHM Delay has run in the new app for quite awhile now but it is my understanding it won’t directly monitor the status of STHM (new app) like it does with SHM in the classic app.
Example:. If you were to disarm SHM (classic app), SHM delay will automatically change location mode to whatever you had set the default to be in SHM Delay. If you were to disarm STHM (new app), location mode would not automatically change to your default setting in SHM Delay. You should be able to work around this but it does change the described behavior of SHM Delay 2.0 in the documentation.
There may be other differences too. I haven’t had a chance to test it much in the new app yet.
The developer of SHM Delay is now running almost entirely on Hubitat so he has stated there won’t be a rewrite for it to work 100% in the new app.