Your initial claim was that the idea of a “necessary” God means we must know he exists. That is essentially saying “God must exist”. Now you talk about conceiving he exists and that suggests it’s still all just in your head and doesn’t actually say anything about reality. This is the difference between the internal logical consistency of the ideas in your head and whether the ideas in your head actually reflect reality.
I'm saying you can't witness a possibility of God as in he may or may not exist, to see God as possible in world x as in the Necessary, you can only do see if you see the REAL EXISTING one. You can't imagine non-existence of the necessary existence it's impossible.