When Cloudflare Proxy is enabled (Free/Pro plans), it imposes a hard 100MB limit on file uploads via POST requests.
Plesk File Manager does not support client-side chunked uploads, so large files cannot be uploaded when Cloudflare is active.
Adding chunked upload support would allow users to upload large files safely even when behind Cloudflare protection, and improve reliability for all users working with large assets like videos or backups.

See: https://developers.cloudflare.com/cache/concepts/default-cache-behavior/#upload-limits