is trump finally showing the world he has dementia?

I think you are perhaps misreading the things he does as "mistakes." I think he has an idea of the way he wants the country to move and he just tries things and pushes until someone says no, then he backs off. Calling this dementia is giving a bad name to those suffering from dementia.

I think some people are just finally realizing it. He’s been doing this for awhile, now.

Trump claimed he bombed the Nordstrom two pipeline from Russia to Germany - but that's Biden. So, yeah, a little.

He is cornered and lashing out at those that cannot fight back.

Amazing how weak our system of government is at stopping a president when they go insane.