Thanks from my side (as well), done!
@pit your postings are important (and inspiring 
to me), so here few things that are related to: sudo journalctl -b | grep 'Operating mode', as @guido.gunther wrote for public use:
where val:
13 - Wi-Fi station + BT dual mode
14 - Wi-Fi AP + BT dual mode
As well (as written within Page 9) explained here:
And this post (thread) is additionally explained how to: Bluetooth not found but service runs no default controller - #17 by joeybronzoni. Just replaced current one (see two red marked lines, as linked, I removed dev_oper_mode=5 line) + wlan_rf_power_mode=0x00:
options redpine_91x dev_oper_mode=13 rsi_zone_enabled=1 antenna_diversity=1 wlan_rf_power_mode=0x00
For above working changes, I’ve used sudo/root rights over JumpDrive connection. Please make backup of the original .conf file, as first step (simply add BKP folder over there, in order not to change owner, and copy+rename original file …).
Partially proofed with:
cat /sys/module/rsi_91x/parameters/rsi_zone_enabled
1
@pit, I’m not there yet (not for real), but still wanted to give some direction that should help you with your BT issue. Take care.