I’d suggest attacking the root of the issue – why the RG is taking so long to load. (I’ve found the articles and book at https://www.amliesolutions.com/ to be the best on the topic).
If it’s absolutely impossible to fix the root issue, then this feels like spinner territory, where you are trying to distract or reassure the user while the RG loads. So you’ll be hiding the RG and showing a spinner until some condition is met. This will take some experimentation to see what works… like a When workflow to show the RG only after the page is loaded, or a condition on the spinner and RG that shows the spinner and hides the RG while the RG is loading.