Struggling to Redeem Miles&Smiles Rewards with Turkish Airlines

I have been a loyal member of Turkish Airlines' Miles&Smiles program for several years. I've been attempting to redeem reward tickets for quite some time now, but unfortunately, the page only displays tick boxes without any visible text. I reached out to the call centers, and they informed me that there are no reward tickets available for the flights in question. I'm curious about the seat allocation process for reward tickets for Miles&Smiles members. Specifically, I'd like to know when THY allocates these seats and what percentage of the quota they assign. Why are reward tickets never available?