I thought something was wrong with the phone indeed, but it was actually Vivaldi. Here are battery stats after getting rid of it:I never noticed such battery draining. Vivaldi runs smooth (better as Firefox) on my two Xiaomi smartphones without any trouble.



Brave only appears on the list one time and it used just 1.14% of battery, unlike what was the case with Vivaldi which used more than 70% when not in use.
It might look like AdGuard now drains battery—it isn't. There aren't many apps that consumed battery overnight and AdGuard consumed the most of it these few apps, so this is why it is first on list.
These are the real stats for AdGuard:


