El Salvador keeps buying the Bitcoin for its strategic reserve. Businesses and citizens can keep using it.
But for getting an IMF loan, IMF (which, to put it mildly, doesn't like Bitcoin) required the end to Bitcoin legal tender status.
Now the businesses are free to accept it or not instead of being required to accept it. That's all. The government plans to keep buying and using it.
The IMF wants to feel that El Salvador (a) will likely be able repay the debt, (b) in a currency that is unlikely to devalue too much. For that reason, the debt would probably be in USD or some other prominent world currency (letting the debt be in El Salvador's local currency would risk them printing money to devalue it, threatening (b)).
So the IMF would probably make the debt in USD. In theory, bitcoin can be exchanged for USD, so in theory, El Salvador could exchange some of their bitcoin into USD to pay the IMF back. But what if bitcoin's value drops precipitously? Or if it becomes illiquid?
It seems the IMF thinks bitcoin is hype, so it expects its value to drop to near zero eventually. That would make it very difficult for a country that has large bitcoin reserves (instead of large reserves of a more stable currency) to repay the loan.