Thanks ! That did the trick. I hadn't realised the spam folder had to be activated for the related icon to be active and visible.
It makes sense, but it isn't indicated anywhere (or not as far as I could find).
Nor can I remember if in a previous version I had activated the spam folder or not - but I was able to see the 3 icons I had activated, moving to spam being one.
Main thing it now works for me.
Thanks again, - I really like using Aqua-Mail on my Android devices, in the absence of a Thunderbird version for Android.