Are there any block explorers that will show you the amount in dollars at the time of transaction?
You have been given accurate information needed. You can use
https://www.blockchain.com/explorer?view=btc or
https://blockchair.com/.
If you use blockchain.com (the first link), the bitcoin sent or received or the block you are checking would be estimated in current BTC/USD pair price. As the bitcoin price is changing, so the value of the amount transacted will be changing based on the recent bitcoin price in USD.
If you use Blockchair.com, the bitcoin transaction would be estimated in BTC/USD pair as at the time the transaction was made, the value will not change to the present bitcoin price in dollar.
You can decide to use which one you think is better for you. Some people will prefer to use blockchain.com explorer just to know the present price of the bitcoin transacted at certain time in the past, while some people will just prefer blockchair.com because it would retain the old price when the transaction was made, just like when solving dispute and estimating bitcoin price in US dollars.