The tile prices have increased significantly, any suggestions?

Or are you referring to my wish for glossy tiles, which I cannot implement due to the lack of options?

Yes, that's exactly what I had read. On smooth tiles, you can see every speck of dust.

Who is responsible for the delays that lead to the deadline expiring?

From a purely contractual point of view, I am responsible. I sent a document somewhat late, which started the 12-week deadline for the start of construction. This deadline is literally a few days beyond the fixed-price deadline. Not a very fortunate situation.. Do you have experience with the same topic?

The general contractor specified a certain tile supplier. I am considering whether to completely exclude the tile from this additional effort.

Only do that if you can/want to do it yourself or if you definitely have a tiler. We did the same because we didn't find anything we liked at the tile supplier specified by the general contractor. Finding a tiler then cost me the most nerves during the entire construction.

When I read that the clay comes from Ukraine, I had to laugh..

Under the guise of Corona and Ukraine, you can really dig much deeper into your pockets.

By the way, our terrace tiles in 45x90 still cost 34 euros per sqm at Hornbach/Union, just saw it live today because I want to build a grill. And maybe make the top plate out of it.