Bild is not currently WP5-compatible. WP5 introduced a rather big shift in technology, and it took me some time to sort things out and come up with a new codebase. 2 days ago one of Mauer Themes’ themes has been updated to fully support WordPress 5 and the new block editor. I will update all the other themes in the coming weeks. And I believe a WP5-compatible version of Bild will be released by the 1st of February. In the meantime, it’s recommended to run Bild on WP4.