Trad IRA/Roth Conversion: In 2021 I invested $10K in a mutual fund. In 2023, I converted this fund to Roth when it was worth $8K. Taxes due are based on $10K or $8K?

@Steverino78 - $8k.   Sounds like you did an "in kind" transfer.  The taxable amount of the Roth conversion is based on the closing price of the mutual find on the day you did the conversion.