After updating my MacBook to macOS 11.3, my "Favorites" disappeared on my iPhone (yes, iPhone). I tried the iCloud trick with turning it on and off on my phone for Safari, and that made them re-appear on my iPhone...but then my "Favorites" disappeared in Safari on my Mac. So it seems like it either works only on 1 device. Very odd issue, hopefully someone has figured out a fix.
What a new tab in macOS Safari looks like now, it used to be full of Favorites:
What a new tab in macOS Safari looks like now, it used to be full of Favorites: