Is there a script for bitcoin core which prints all spendable UTXOs given a private seed? I am looking for an open source script or application which would take a private wallet key from the user (from terminal input or file, as mnemonic or xpriv string) and then connect to a bitcoind and output all UTXOs which are owned (spendable) by that key. Does something like that exist?
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 &lt;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.