There is a question where someone answered topsites://:
Open Favourites Page in Safari with Javascript
Is there any text which navigates to favourite bookmarks? Like favourites://?
I don't use Top Sites because it's so messed up and preview images are never correct and I want to change the homepage to the favourite bookmarks.
Best Answer
If you just want to set the favourites as the home page, you can do this from Preferences → General: set ‘New windows open with’ and ‘New tabs open with’ to ‘Favorites’.
There doesn't appear to be a URL to navigate to favourites. When I wrote my answer in your linked question,
topsites://went to the favourites page if that's what you had selected, but nowadays it doesn't and there doesn't seem to be a replacement.