The situation I have in mind is the following:
An epic battle ensues between a Young Green Dragon (caster variant) and a Purple Worm. The Purple Worm swallows the dragon; meanwhile, the dragon has blindsight and can cast Command.
Command is a spell that requires you to see the target. However, the dragon is Blinded (so it can't see) while swallowed. It has blindsight out to 30 ft, though, so it can perceive its surroundings without relying on sight.
Can the Young Green Dragon use the Command spell to have the Purple Worm retch it out?
The general question is: does the interaction of the Blinded condition with blindsight still prevent the caster from using spells that require them to see the target?
There is another question which asks if creatures with blindsight can be affected by the Blinded condition. The answer is yes, and we begin this question with the fact in mind that the caster is both Blinded and has blindsight.
Best Answer
A Blinded, Blindsight-possessing caster can still cast its sight-dependant spells
The Blinded condition is defined as;
while blindsight is written as;
A creature with blindsight does not require or rely on sight within the specified radius so the first aspect of the blinded condition is nullified within the region of blindsight. the second aspect however is not directly countered.
RAW a creature with blindsight can still do anything that requires sight within that range including casting spells, but would have disadvantage on attack rolls due to the blinded condition.
creatures that have no eyes such as oozes are already immune to the blinded condition so there shouldn't be any issues with the inherent logic with them. but a creature with blindsight that is blinded (such as the aforementioned dragon) would still be worse off than one that is not blinded.