SmartThings is in the middle of a transition to a whole new architecture.
In the past, SmartThings offered a free cloud service running the groovy programming language. Customers could upload both custom Device Type Handlers and custom SmartApps to their account in that cloud and they would appear in the SmartThings app and would run as needed.
Under the new architecture, that cloud service is gone, so none of the old code will work. During this transition period, some old stuff customers had previously uploaded will keep running for a little while, but you are no longer allowed to make changes or add any new groovy code.
Under the new architecture, Groovy device type handlers will be replaced with Edge Drivers written in the Lua programming language. These will run on your own hub.
For automations, it’s a totally different picture, and it’s complicated. I don’t want to go through it all again here, so please read the following two threads and they will answer that question. (The topic titles are clickable links)
But the short answer is you can no longer upload groovy SmartApps to your account. Instead, contact the author of the smartapp you wanted to use and ask them if there is an option for the new architecture.