For field, GIS and distributed systems, opening the application without connectivity is only the visible part of the problem. The real architectural complexity begins when the same entity can change in two independent replicas.
Identifiers, versions, change journals, synchronisation rules and conflict policy need to exist by design. It is equally important to explain to a user why two versions differ and what decision the system is going to make.
Offline-first is therefore better treated as a property of the data model and project lifecycle rather than an extra UI mode. Designed this way from the start, a system can tolerate unstable connectivity without silently losing control of its data.