The error message:

error checking existence of ssz-encoded file 21954318 for checkpoint sync init: 
stat 21954318: no such file or directory

means that Prysm is looking for a local SSZ-encoded file representing block 21954318 in your local data directory — but it's not there.

If you use --checkpoint-block and --checkpoint-state, Prysm expects local SSZ files with the corresponding block and state data to be present. The error occurred because those files don’t exist locally.

Use --checkpoint-sync-url instead to sync from a remote trusted source (like Lighthouse or Teku), without needing local files.

Example:
./prysm.sh beacon-chain \
  --checkpoint-sync-url=https://mainnet.checkpoint-sync.ethpandaops.io \
  --force-clear-db

Only use --checkpoint-block if you already have the .ssz files locally.