Maybe it’s the same solution from here:
this doesn’t work
adb shell dumpsys window windows | grep -E 'mCurrentFocus' | cut -d '/' -f1 | sed 's/.* //g'
this does:
adb shell dumpsys activity recents | grep 'Recent #0' | cut -d= -f2 | sed 's| .*||' | cut -d '/' -f1