However, this won't work if the page is using virtualised scrolling (common with React et al. SPA for performance reasons, to avoid huge DOM trees as the page expands). The majority of content that is outside of the visible window will simply be unmounted from the DOM.
I'm not sure what the best-practice for a webapp designer is here? Perhaps intercepting Ctrl+F and displaying a custom search that will do the correct filtering on the back-end and update/retarget the view? Azure DevOps does this but it's still frustrating if your focused element is not within the capture point for the event.