STHM - Custom Monitors - Where is it?

the new app has a region lock on some smartapps outside the US which the Classic app did not have. so, if you are outside the US, i imagine STHm is blocked to you.

always contact ST support and request that service be enabled and perhaps if enough users respond, they might open it up eventually.

without STHM, i guess you can try to use automations as best you can.