Migrate the app to support strict concurrency for Swift 6

[itsmeichigo]

We should check errors when strict concurrency is enabled to get ready for Swift 6.

Internal discussion: paaHJt-6zU-p2

[dangermattic]

🚫 Please add a type label (e.g. type: enhancement) and a feature label (e.g. feature: stats) to this issue.