Can you use a block editor in gallery post?

I have a question regarding gallery post types. I am currently using the “Galley” post type to list various business clients (instead of the client post type) because it permitted me to have more flexibility such as adding categories, content for SEO, and a featured image. However, I am only able to use Classic Editor tools and am not able to use widgets. I would like to add html code to the gallery post to add a contact form for individual clients in a sidebar widget.

Is there a way to add the block editor (i.e. Gutenberg) to the Gallery Post Type to permit me to complete the functions listed above? I am trying not to change the theme if possible. I am not a techie so any input or suggestions are appreciated.