Yes, but you'll probably need to know some javascript.
If the Confluence site is overriding the keydown event using a JS event listener, you'll need to write a userscript which will remove the event listener so the functionality is restored to the captured shortcut.
I haven't used Confluence, but if Atlassian has overridden the Find command ctrl+F / cmd+F, that is very bad behavior on their part and the best course of action is to contact support and complain about that bad UX.