Incapable
Incapable is an adjective that denotes lacking the ability, power, or means to do something. It can describe a person who cannot perform a task, or an object or situation that cannot be achieved under certain conditions. The term is usually used for a specific limitation rather than as a general judgment about overall character.
In everyday language, incapable is not inherently insulting, but it can come across as harsh if used
Etymology and forms: incapable derives from Latin incapabilis, from in- “not” + capabilis “able to be held