According to this (via this post) there are configuration values for that.
While excellent in details compared to many other posts on the internet, that EFF article still leaves me with some questions. GSM can run A5/3 and A5/4 crypto, at least the latter of which should be just fine, but might be that it is rare in reality. And as they say between the lines 3G/UMTS isn’t that much better in the authentication department (they have the same-ish core network after all). With prefer 4G/LTE already being a thing, I’m not entirely sure what the improvement is. (although that is not really viable for us until we get VoLTE)
If my repo-sloughing serves me right, the radio HAL version mentioned in the article is not something that SFOS supports though (understandable, with it being an Android 12 thing). But i wonder what the difference there is compared to current possibilities.
Edit: some sort of insight to the change in 1.6:
https://android.googlesource.com/platform/hardware/interfaces/+/master/radio/1.6/IRadio.hal#349
They are changing from preferred to allowed apparently, not that i understand how the modem would ignore the preference with anything less than CSFB, if even that.