bitcoind – Is there a script for bitcoin core which prints all spendable UTXOs given a private seed?

You can import a descriptor composed of the xpriv(s) (or xpub(s) if you just want to watch the coins) to the bitcoind wallet, and then rescan the block chain for transactions involving derived key up to a configured gap limit.

For importing the descriptor, use the importmulti RPC call in versions <0.21 and the importdescriptors RPC as of 0.21 (upcoming).

Both calls allow you to pass a creation timestamp in order to rescan the block chain from this point. You can otherwise manually call rescanblockchain.
Note that, depending on the number of blocks you are scanning, it will take some time. You can monitor the progress in your debug.log.