Mids Ive been thinking a lot about this question of yours.
tldr: news should be The Varnished Truth.
a) News should be impartial and as full as possible so we should see any Russian victory and gain some knowledge of any Ukrainian casualties
On the surface this seems the best. Don't treat your population like children. Don't hide the shit. But ... that doesn't take into account human nature. Morale in war is very important. Especially in a democracy the more people are unhappy/discouraged, the more there will be a desire to disengage and being a democracy and with an eye on re-election, the politicians will be influenced. They have to be, or it's no longer a democracy.
But as a mass we can be affected by bad news and by good. The will to carry on might waver if there is bad news, to the point of people saying "well we shouldnt pour more materials and effort into a lost cause". Yet if those materials and efforts can help the, let's say, Serrenland's (made up name!) army through a rough time then it's worth persevering, and a temporary loss can be overcome and things go better. Or the losses might mount and the Serrenlanders fail. Or the resources sent could allow thousands of people to be evacuated to safety, so even though the war is lost a great deal was gained. That becomes clear in hindsight though, whether or not it was worth keeping going. But making a decision to withdraw based wholly on the mass mood when something is going wrong is a bad idea.
It's clear even from these threads how terrified people are by the very idea of nuclear explosions. That degree of terror is not reasonable. Understandable, but not reasonable (anxiety is a bitch). Any nuclear attacks are not going to be the first recourse; there are extremely skilled people working to make sure it doesn't happen, and one nuclear device going off is not the same as the end of the world. But people are scared and in the end Putin is using that fear and it's working.
So clear heads need to decide. Feelings are great motivators but not always sensible or wise; they need to be governed by thought.
Another factor is that people in charge have much more info than most people in the country do. Not all that info can be shared for obvious reasons, you don't tell the enemy about the best weopons you have or your strategic plans.
Some information can be literally true but on its own present a partial or wrong picture. The old adage of the blind men and the elephant's tail and trunk and feet applies.
So I don't think that the full truth is a good idea.
But.
b) We are allies to Ukraine and our media should refrain from highlighting any Russian success as it could act to reduce Ukranian morale and give Russia information about Ukrainian weaknesses. We do not want to be inadvertently part of any Russian propaganda exercise in addition.
Just cannot go along with this. We are not, as a country, very wise or steady. But I don't think we should be fed happypap either. The amount of information provision has risen hugely in the last decades and, thank god, independent information provision at that. But the level of mass analytical thinking eg at university has gone down compared to 40 years ago (at least so my older university teacher-friends tell me). (Damn you, Murdoch, you evil man). But it doesn't mean we should just go along with feeding only good news, however much easier that is to hear emotionally. The govt should at least try to treat us as people who can and are able to take in some bad info. I regard the role of a govt as being to govern but also to try to raise standards, not allow them to sink to the lowest emotion-driven level. Of course that's a bit hard with Bojo in charge ... }
So the news needs to be a balance between the hard truth and happypap. But for me, the balance needs to be rather more on the side of truth than propaganda.
There are many many more factors you could add in here but it's already way too long a post =) (also ive got a headache, sorry if it's a bit of a messy post)
But to sum up again
TLDR - the Varnished Truth.