I tested and synched something in a seperate Ankiweb account. After that I deleted all notes, did “Check database” repeatedly an both sides, Mac and iPhone, synched repeatedly and did the login/logout and browser refreshing repeatedly.
On Ankiweb it still shows 105.58MB.
On Mac and iPhone I’m on the latest release.
Why is that? How can I get it straight?
What do you expect to happen? That AnkiWeb shows 0MB?
Here’s what Check Database does:
For Anki Desktop you can use Note Size addon to analyze the collection size. But it doesn’t show information about Anki Web.
Thanks for the surely well-meant guidance.
I would expect, that after I deleted say 99% of notes in a local collection and synched it to Ankiweb, the collection on Ankiweb wouldn’t have the same filesize as before.
You might not have noticed, that for that case in the forum there had been several times the recommendation, to use the “Check Database” function for.
I already used that for that in the past.
Thanks. I’ll have a look on it and a try too, I think. My actual problem is, that Anki has a file limit for synch with Ankiweb. It’s different for compressed and uncompressed. To be on the safe side, I always look directly on Ankiweb. And that’s where my problem began. 
Tried the plugin. Great. Thanks.
I got a hint outside the forum: Forced synch is the solution.