I know Obsidian provides the ability to set different themes between different libraries, but when I open another library, the themes and settings such as shortcuts for my usual library are all unset, which is too much trouble for me.
Proposed solution
There should be an option to synchronize themes and Settings. When this option is enabled, changes made to themes or Settings are automatically synchronized.
Alternatively, some Settings should be global, like shortcuts, that I don’t have to set repeatedly.
I don’t understand, what is “librairy” for you? Do you refer to vaults in Obisidian? You can simply copy-paste things that interest you from the “good” [.obsidian] folder to the “not so good” [.obsidian] folder, from theme to plugins, snippets, keyboards shortcuts. I don’t even set up anything while moving or creating a new vault : I copy paste the folder from an older one.