A sentence that stays faithful to the whitepaper you are teaching — the opening line, and section 9 (combining and splitting value):
"The law can tell a shop it must take bitcoin, that it may, or that taxes are only in dollars. None of that writes or erases the coins in your wallet. Those are unspent outputs you spend by signing them; a statute only says what a cashier is allowed or required to accept."
Section 9 is already the picture you described: a payment is one or more inputs plus, normally, two outputs — one to the recipient and one back to you as change — not a bank editing a balance.
https://bitcoin.org/bitcoin.pdf
On the El Salvador facts you named: IMF press release PR25/043 (Executive Board, 26 February 2025) says the prior actions "include legal reforms that have made acceptance of Bitcoin by the private sector voluntary and ensured that tax payments are made only in U.S. dollars."
https://www.imf.org/en/News/Articles/2025/02/26/pr25043-el-salvador-imf-approves-new-40-month-us1-bn-eff-arr
That is the "state allows it" layer. The "I can still use it" layer is section 9 plus the abstract: payments go from one party to another without a financial institution, whether or not a shop is legally required to take them.
Not professional legal advice.
