Time machine not enough space for backup

So I have this time machine, connected to my LAN, and an iMac also connected. I believe back then I paid a hefty sum for the seemingly unsexy task of just backing up my memories now and then on the shiny TM.

Now, the gear icon in TM disappeared so I cannot delete old backups. Then Apple says "you never have to, so we will be smarter and delete the option for you".

So why is my disk now saying it is full then? Obviously it is not working, that the TM decides for itself that old files need to be deleted.

This issue has been reported before, but with no answer from Apple.

Could that be because they want you to store everything in their cloud and not on a local disk? So that you send your 1000Gb over the internet, which is disgusting in itself if you think how much electricity is wasted by that?

Apple, please tell us how to get the time machine to work again. I dont care if we delete all old backups, I only need a good last one.