One question...

Theme: Symbol, component in schematic

How can I move a finished circuit section to another schematic page?
"Of course, I didn't realize this until now, when everything is already routed on the PCB side. I would prefer not to lose that part and not have to redo it. Is there a way?"

Yes
: Select the desired circuit section e.g. with a catch window. The symbols together with their connections. In the menu "Edit" use the item "Move onto another schematic page...". Done.