It won’t go into effect until 10 years from now, so the effects on those poor countries won’t be felt until long after Biden is gone.
Ireland made it so it said 15% instead of at least 15%, so it can’t be adjusted later, and the global average is already at 20%. So basically it will do nothing for the rich countries like the US where corporate tax rates are already the highest in the world while bankrupting poorer countries as they implement these measures.
Not only that, it has no chance of passing in the US and most of the unstable countries that signed onto this will reject it as soon as they notice the deleterious effects of raising taxes on the production.