Probably the best place to start on the move away from Groovy is the community FAQ on edge Drivers. It also includes links to all of the official announcements if you just want to read those.
But the short answer is that the old architecture depended on a cloud that smartthings provided, and that had reliability issues. (It probably also ended up being too expensive for Samsung as the number of smartthings customers grew, but they haven’t said that officially.)
Although the new architecture is still largely cloudbased, a lot more stuff can run locally on your own SmartThings/Aeotec hub if you have one. But because they are making this change with the existing hardware, and those are actually pretty limited devices, they switched from Groovy to Lua because Lua is a more “lightweight” language, and would run more efficiently on the hub itself. Lua is used for a lot of mobile gaming, for example, for just this reason. It’s also been used for years by some of smartthings’ competitors in the home automation space, including Vera.
Anyway, that part specifically was discussed in one of the announcements.
Announcement | SmartThings Edge for Devices and Automations
And here’s the community FAQ, which gives both the details of how you use the new architecture and links to the announcements for an overview of what’s going on. 
FAQ: I have no idea what Edge is. Is that a new developer tool? (2022)
I know it’s a lot to take in: I hope that gives you a place to start.
Meanwhile, I’ll let others discuss the reporting options for your temperature sensors. 
