Not sure where you guys are getting the info about BtSsm not working with OBDLink devices. Its a mystery.
I was the original tester and power user back in 2014/2015, who worked with BtSsm developer on all new features and beta testing, helped add TCU support and experimental CAN support, etc.
The software most certainly supports OBDLink LX and MX series devices (no longer remember which revisions and up and which firmware and up).
Worked flawlessly in Kline and CAN mode on my 2010 and still works on a 2015-2019 WRX in CAN mode today.
Android 5/6/9/10, maybe others too, didnt use so cant confirm/deny.
Best solution for older Subarus is Tactrix OPv2 + wired USB OTG to phone and BtSsm protocol/connectivity option to reflect the same, but if you need wireless, OBDLink LX/MX should be fine.
Active dev of BtSsm stopped a few years ago as the app was and is feature complete for older gen Subarus.
Newer ones have moved away from SSM and to E-OBDII rendering the app useless for those.