However, I had to migrate a Vue 2 + TS app to Vue 3 and their guide at the time was pretty underwhelming. Props to Evan for dedicating time to migrate a sample app and publish the migration as commits, but the app was quite basic and dependency-free so I had to figure out a lot of stuff on the go. The compatibility build actually slowed down my progress as it took me a lot to figure out that I didn't actually benefit much from it and could just drop it. Till this day I don't have a clear idea about what @vue/compat is for.
Hopefully, with them pushing Vue 3 as the new default, there will be more detailed how-tos available.