Hello,
I deleted Backblaze's online backups and restored my previous iCloud preferences. I reactivated Time Machine backup. I used Terminal to purge unnecessary files.
My system (MacBook Pro M1, 16 GB RAM, 1 TB SSD) now appears to be operating within normal parameters. No evidence of hardware degradation or storage performance issues could be detected (SSD read/write speeds exceed 2 GB/s; disk health 100%; ~300 GB free space available). The “System Data” is currently elevated at approx. 100 GB, including 59 GB purgeable. The lower-than-normal performance rating is apparently attributable to a transient, resource-intensive background workload initiated by recent iCloud resynchronization and large-scale file reprocessing. The system is concurrently performing Spotlight reindexing (15 GB index), iCloud file synchronization (via cloudd, fileproviderd, bird), and metadata/PDF rendering operations (CGPDFService) across a dataset of approximately 10,700 PDF/EPUB files. I expect these processes to be completed within 24–72 hours.
Thanks again for your helpful suggestion.