I have just replied to the BT Wifi feedback with the following message.
-------------------------------------------------
just checked the app on google play and the 'more about the app' does say that you need android 10 or above for the app to work
Solved this myself - no help whatsoever available from BT but I'm a new customer so I imagine you all know that already. Alas, my solution is no longer available!
The old app, which I am using on Android9 and which works v well, was on APK until June but has now disappeared in favour of the Android10 ones only - utterly berserk. APK was the only safe site I found while searching but it may help that our app ends in 8.0.4 (new ones 8.0.10 and 8.0.11).
The dead address that worked for me is not even on Wayback: https://apkcombo.com/bt-wi-fi/com.bt.mnie.wispr/download/phone-8.0.4-apk
Good luck and I'm very sorry for not posting this when it worked, amid my enduring other frustrations with BT.
This claims to offer 8.0.4 but I have no idea whether Aptoid is a safe site, so BEWARE: https://bt-wi-fi.en.aptoide.com/versions
Same here: https://www.9apps.com/android-apps/BT-Wi-fi/
Note that another offer imitating APK was blocked by my Malwarbytes: es.aapks.com
BEWARE, again, and good luck.