One way to limit exposure to negative news is a keyword filter, which I implemented 6 months ago, early on in the project: piefed.social/post/7576
avoidance is generally considered harmful for mental health, what would be better is giving users the ability to curate their information diet, news sources should be trustworthy , display rational reasoning which might help users learn by observation (aka observational learning) , this will be helpful for mental health and mental fitness because rational thinking is associated with mental health.
multireddits could help with that because instead of getting just news about ukraine/israel/sudan/iran from a general community, you could get it from communities specific to those conflicts , the people subscribing to these communities are probably more motivated to discuss it so they will generate more rational thinking (which is more effortful so it requires more motivation).