Around 2020, SmartThing began planning for a new architecture, and by 2023 a lot of the work was done and they began turning off the old architecture.
Gone were groovy device type handlers, also known as DTHs. (Replaced by Edge Drivers.)
Community FAQ:
FAQ: I have no idea what Edge is. Is that a new developer tool? (2022)
Gone were custom groovy SmartApps that ran in the SmartThings Cloud. This broke some thirdparty integrations as well.
Community FAQ:
Why Did My Integration/SmartApp Stop Working in January 2023?
Gone was the IDE, replaced by a new web interface:
Life after the IDE: Questions and Answers
All of which is to say if you are reading posts dated before 2023, the ideas and general approach may be fine, but any step by step instructions are probably out of date.
Look for a newer thread (there probably is one) or ask in the forum for new instructions. If you try to follow older instructions you’ll probably just get confused.
See the links above for more details. 