USD value at time of receipt for income taxes, USD value at time of disposition and the delta for capital taxes.
The nature of the transaction’s purpose determines where/how it is accounted for. Just like with usd its up to you to determine if a transaction was a deductible expense, capital gains/loss, charitable contribution, a non-tax event like an in-kind investment, bond/credit/borrowing, income, vesting… its not different enough to really be having this conversation to be honest, but I’ve heard it all over the past decade so fire away.
I just make notes of the usd value transferred at the time, to simplify things when filing taxes. But the block explorers often show usd dollar values at time of transaction and time now so its easy to have a record to look at as well.
Some exchanges are beginning to attempt doing this for people, making tax forms like stock brokerages make tax forms, but they all assume people are buying and selling crypto on their platform instead of earning it directly off platform. Swing and a miss there, but lets check back in 5 years.