Still having problems here. Can the character be the plot of poem?

Question

No. The plot is the story told. It can evolve around a character, but the character is not the plot.

Remember Cinderella? The plot is not her, it is about the fairy tale change in the destitute life of a girl from almost slavery to being a queen.

I also thought of Brownings "Soliloquy of the Spanish Cloisters", which reveal much about the character of the speaker, but the plot is not the character, even as strong as he is in the poem, the plot is about how we reveal moral character. You might read that poem, a strong character study on the face of it, before one looks in the mirrow.

In brief, the plot is the story line. What the "problem" is; what is done; how it all turns out.