it makes no sense to switch from Vivaldi to Brave lacking any customization, with Vivaldi you can customize it as much you want, if you don't want, nobody forces you to, with Brave you don't have such option

I am still on Vivaldi and instead of switching from Vivaldi to Firefox I gave a try to uBlock Origin Lite and seems to work fine, the UI is much worse than uBO (I am especially missing easy switch to turn it off completely instead of disabling extension in browser settings), but can live with it, as much as I dislike Firefox (using it on mobile though) it's the only alternative I would move to from Vivaldi on desktop