At many international airports, once a passenger enters the "sterile" transit or departure area (airside), they are physically separated from the arrivals flow. In some airports, it is simple to walk back toward immigration/baggage claim, but in others, the architecture creates a "one-way" system where exiting requires a security escort or airline intervention.

How can I determine if an airport allows passengers to exit the transit/departure area after entering?
Details:

This is particularly relevant for long layovers where a passenger might enter a transit lounge for a few hours but later decide they have enough time to visit the city.

Aside from searching for specific "trip reports" for every individual airport, what are the reliable indicators or research methods to determine an airport's "exitable" status ahead of time?

E.g.:

• Terminal Design Terminology: Are there specific architectural terms (e.g., "separated flows," "sterile transit hubs") that indicate a one-way path?
• Map Cues: On official airport maps, what visual cues or labels (e.g., "no-return doors," "exit lane breach control") should one look for that suggest a path from the gates back to landside is restricted?
• Regional Standards: Are there specific regions or aviation authorities that mandate a physical separation between departing/transiting passengers and the arrivals hall?
• Official Guides: Do airport websites typically list this under a specific heading (e.g., "Transfer Information" vs. "Arrivals")?

I am looking for a way to identify this "point of no return", ideally during the planning phase (ideally, before my trip), so I can decide whether to go through immigration immediately upon arrival or head to a transit/airside lounge first.

All airports require you to reclear security once you leave airside. Most will often have a transfer zone to go from arrivals directly to departures (many will also require you to re-clear some form of security). Your best bet is to ask in the relevant country forum when researching your trip (which you should do to determine if you want to attempt going into town). Keep in mind the process can change depending on process and how they structure their airports.

Agree with the above on asking in the relevant destination forum. Be aware in some countries/cities it is illegal to access the departure flow without the intention to depart (SIN, most notably of the major destinations).

Be aware also that to leave the airport, you'll need travel documents sufficient for a (tourist) visitor, which can be more than the requirements for a transit (which would have been checked at check in and/or your first flight's departure gate). There might also be a VOA fee, etc.