Yes, I can confirm FreeWifi_secure functions on FP3+ with FPOS (I’m running 8901.4.A.0012, Android 11).
However, I’m running /e/ (0.23) on a FP2 and it does not work in this configuration. One of my reasons for the FP2 is to prepare a move to /e/ on my main FP3 but this is a bit of a blocker. I’m happy to help with testing or in any way I might be useful. Though I’m partly a developer I haven’t worked on Android (yet 
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This is not a problem for me, I can select the SIM alright, (in fact it gets selected automatically as there’s only one) but the phone then endlessly attempts to connect.
Here’s a link to a conversation I’ve had in the FP forum. In 