> doesn't the IMF use a basket of currencies called SDRs instead of dollars
Yes, which are just claims on that basket of currencies, the U.S. Dollar being the majority currency (in the current 5 year basket 43.38% with the next closest being the Euro at 30.93%). My point was admittedly hyperbolic, but as the majority currency in the SDR basket (and the world reserve currency) the USD has both voting and trade sway as countries need it to pay debts and acquire resources.
As for governance, U.S. votes account for over 16% (the greatest shareholder of votes) with the next closest being China at 6%. In effect, the U.S. has a soft-monopoly over the basket as the stated requirements for ranking/inclusion "take into account their current prominence in terms of international trade and national foreign exchange reserves."
Combine that with the U.S. military/intelligence threat, NATO threat, and all of the other tentacles of U.S. hegemony and its currency is—for all intents and purposes—a weapon.
Something like Bitcoin is a significant enough threat that the IMF as steered by the U.S. is incentivized to dismiss it (and has [1]).
As for El Salvador's holdings, well, yeah. Even as a Bitcoin maximalist I'd think Bukele were putting his country in a dangerous position short-term if he went all in as other countries would just threaten to cut them off from resources/aid (see link which makes my point).
A full-blown transition to Bitcoin is going to need enough countries with tradeable resources to start accepting it as payment. Again, we're in the early days of the transition away from state currencies. The real battle will be when they try to rug pull everyone with CBDCs [2] (which is precisely when the intelligent but timid will realize that Bitcoin is the only option to preserve personal/state sovereignty).
[1] https://www.ft.com/content/fbf9aef0-453f-4e61-bd83-ff2b2bc92...
[2] https://twitter.com/martybent/status/1537946342890168323?s=2...