I'll try to answer my own question :-)
tl;dr
This seems to be a misunderstanding. With Android 11 or later, cell broadcast messages for emergency warnings are pretty much guaranteed to work, but they work on many devices with older versions, too.
Source of the claim
This claim seems to be based on a misunderstanding - probably some press release that got misquoted or incorrectly abbreviated somewhere along the line.
It is unclear where this claim originated. Many news sources have published it (see links in question), but the sources I found all do not attribute the claim, and use similar wording, so they probably copied it from some press release or article somewhere. The official site of the responsible German government agency (Bundesamt für Bevölkerungsschutz und Katastrophenhilfe - https://www.bbk.bund.de/ ) does not mention Android 11 specifically - instead, it lists individual phone models that are or are not supported (Kann mein Gerät Cell Broadcast empfangen?).
Technical details
- Each Cell Broadcast message contains a "message identifier" or "message ID" (also called a "channel" on some phones), a number from 0-65535. That message identifier tells the phone the type and content of the message, such as a weather report, a technical message, or a warning message.
- For emergency warnings, specific message IDs have been reserved for different types of warnings, in particular IDs 4352 – 6399. The technology, along with the message IDs, is contained in the standard ETSI TS 123 041, at least since version 9.2.0, published in January 2010. The new German warning system, specified in the offical standard Technische Richtlinie DE-Alert, basically follows this standard.
- Support for emergency warnings via Cell Broadcast mainly requires that the phone reacts to Cell Broadcast messages with these message IDs. The offical Android source code has supported these emergency warning message IDs since at least V4.2/Jelly Bean (see source code).
Conclusion
The offical Android source code (as published by the Android Open Source Project) has supported cell broadcast emergency warnings with the standardized message IDs since at least V4.2/Jelly Bean, so in principle emergency warnings should work at least with all phones running Jelly Bean or later..
However, phone manufacturers (and even mobile network operators supplying phones to customers) can and do customize the official Android source code they put on their devices. It is possible that some of them removed or deactivated warning messages, either entirely, or specifically for German phone networks, as these warnings were not previously used in Germany. For example, on older Samsung phones warnings are supported, but must be manually activated (offical Samsung page).
This changed with Android 11. Before, emergency warning support was part of the general source code, which manufacturers modify and ship to end users. In Android 11, a new Cell Broadcast module was introduced. While the actual functionality seems mostly unchanged, the new module can be updated individually by Google via OTA updates (specifically as an APEX package). That means Google can push updates without requiring a complete Android OS update, and independently of the manufacturers (who may not want to provide updates for old phones).
That means that phones which
- run Android 11 or later, and
- are up to date with Google updates
are practically guaranteed to support emergency warnings, as Google has provided a suitable update. However, many phones running Android 4.2 or later also support these warnings.
Check settings
To see if your device supports warning messages, check Android settings, or the message app settings (depending on device).
If the configuration is available in the settings (look for a section called "emergency alerts" or "wireless emergency alerts"), and if the alerts are activated there, the phone will most likely support the warnings (unless the manufacturer made complicated changes, which is possible but unlikely).
