So this is pretty interesting (and potentially extremely confusing for audiences), as this news can be read one of two ways...
1) Either a standalone Clayface DCU movie is now official, and separately, what would be a different iteration of Clayface is ALSO now heavily rumored to be the/a villain in The Batman Part II...
... or, more likely...
2) A standalone Clayface movie has just been officially announced as part of Matt Reeves' The Batman Saga, set to start shooting "early next year," a movie that will serve as an introduction to/origin story for Clayface, who will also then appear as the/a villain in The Batman Part II. In other words, Clayface releasing in the first of half 2026, with The Batman Part II releasing in the second half (October 2, to be exact).
Again, I think it's almost assuredly the latter, considering Matt Reeves is producing the Clayface standalone movie, but the wording in these articles is not clear at all...