I don't know how proficient you're with the UTXO transaction model that Bitcoin uses. UTXO is Unspent Transaction Output. You can only spend unspent coins from previous transaction outputs. And an UTXO has to be spent in full, therefore usually the need for a change coin transaction output which returns the excess of spending one or more UTXOs in a transaction.

So, if you want to send a part of your coins to another address that belongs to you (or someone else, doesn't matter), you need a second transaction output that sends the rest of your coin minus fee back to a change address of your own wallet.

If you somehow deliberately removed that change coin output from your transaction, the rest of your spent coin becomes the transaction fee.

Transaction fee equals sum of transaction inputs minus sum of transaction outputs.


Agreed.

Your transaction input is of high value to you and you don't thoroughly check your transaction details? I must assume you have no idea of the UTXO transaction model.

I do use Sparrow wallet occasionally, too. I don't see a reason why Sparrow won't create the transaction in the most common way: one (or multiple) transaction inputs, sum of transaction inputs is sufficiently large to cover the desired amount of coins to send to the target address, desired amount to be sent to the destination address AND a change coin output returning excess coins back into your own wallet.
How could this gone wrong if you haven't deliberately, maybe unknowingly, interfered?

Likely any blockchain explorer will tell you who mined the block where your transaction was confirmed in. Contact Foundry as others told you with a Bitcoin signed message, signed with the private key from your transaction input. You can also prove that you own the transaction output address with another Bitcoin signed message from that private key.