Qt Creator 4.12+ cannot build and deploy to android on Ubuntu 18.04

Deploying to android fails with
"No target architecture defined in json file"
(which is indeed missing).
Adding it manually then fails with "unable to find executable".

the very same setup works on Ubuntu 20.04

Setup:
creator 4.13b2
android-studio downloaded sdk -> then completed in qt-creator (downloaded the missing components)
ndk -> ndk-bundle from the sdk

Qt 5.15 built from sources (with the same script), for single abi, armeabi-v7a

Tested with new empty qt-quick application. Ubuntu 18.04 fails also to initialize gradle.
I also tried to remove ~/.config/QtProject altogether, with no luck.