Upgrading a hybrid VaadinHilla 23->24.1 almost works

After a day of fixing all sorts of smaller things, settings, a whole bunch of vaadin:dance and catalog deletions; there is one (hopefully) final thing that I can not get to work. And it is quite central… That is grids in Vaadin-parts. Getting the following error on all grids, even those withot specific LitRenderers:
Uncaught TypeError: window.Vaadin.setLitRenderer is not a function
at GridColumn.eval (eval at Tt (FlowClient.js:1043:101), :3:36)

Frontend/generated/jar-resources/lit-renderer.ts is there with the definition of this missing method. No other errors in Console/Network in browser, and no error whatsoever on serverside.

Any pointers on what to look for is highly welcome.