Do capitals and lowerscases matter in a name?

[_Ghost_]

What i'm asking is in a Minecraft name can there be a like "Harry" and a "harry" at the same time?

 

[Sparko]

no

 

[Candid]

They do not. However, you can change the capitalization of letters in your current name through name changes and some accounts are actually duplicated. Check out this threat for more information: https://www.mc-market.org/threads/452311/