Maybe as a stopgap, you can try cleaning up the auto-generated variants (alternate-size thumbnails) that pict-rs has stored? Might get you under whatever threshold was tripped while supports works out the main issue.

https://git.asonix.dog/asonix/pict-rs/#user-content-api

DELETE /internal/variants : Queue a cleanup for generated variants of uploaded images.`

If any of the cleaned variants are fetched again, they will be re-generated.

My instance is fairly conservative with media uploads and cached thumbnails, but it shaved off a few gigs that had accumulated over 6-7 months. Heads up that the call to that endpoint will return immediately as it just queues the job in pictrs.