You might also be interested in the R-multiverse built on top of R-universe.
ropensci.org/commcalls/r-...

Yeah, it's usually possible but not always obvious where to put _targets/. And then if your app has multiple users and each user has many sessions, you have to manage a whole file tree with many _targets/ folders. This is a general issue for any stateful app, not just apps that use {targets}.

Persistent state (on disk) and user session management are tough in general for an app. Here's a simple example with {targets} and Shiny: github.com/wlandau/targ....

Some Posit Connect instances offer persistent storage in /mnt, e.g. github.com/sol-eng/targ.... The specific path(s) could vary.