The record before 2018 was block [409,069](https://mempool.space/block/000000000000000001569ae442a9081b2da0d7813b4af8c8999e830c39ece1eb) in which 23,642 outputs had been created.

I found these blocks by [sorting blocks per their output counts on blockchair](https://blockchair.com/bitcoin/blocks?s=output_count(desc)#f=id,hash,time,guessed_miner,transaction_count,output_total,output_total_usd,fee_total,fee_total_usd,size,output_count)

Murch

 claims the record then was 13,000 outputs, but they don't link to a transaction, so it's not that useful.

bitcoin

Is custodial bitcoin really worth anything?

Scoresby

This [2018 Coinmetrics article](https://coinmetrics.io/batching/#:~:text=Additionally%2C%20each%20transaction%20can%20have,20%2C000%20inputs%20and%2013%2C107%20outputs) claims the record then was 13,000 outputs, but they don't link to a transaction, so it's not that useful. 