Thanks for the response, but I don't see any filter. I did the cleaning steps in the Geberit video (skip to 2:24).
Here's the part from my toilet.
PXL_20210502_113832299 by TurnOfTheScrew posted 2 May 2021 at 5:48 PM
I have a toilet with concealed tank (tiled into the wall) and Geberit mechanism. It's gotten very slow to fill, so I popped it open and gave the mechanism and seals a clean. It made no difference.
I'm a little puzzled as it simply drip fills, regardless of whether the float arm is up or down...