There's !climatehope@lemmy.world - however it's not super active, but you can be the change you want to see in the world!

I know it's paywalled but Washington Post has a Climate Solutions category that tends to have a little more uplifting coverage - not 100% positive, but usually with a flare of "and here's how we can fix it".

https://www.washingtonpost.com/climate-solutions/

I enjoy checking in on this site when I need some nice news:

https://reasonstobecheerful.world/

Edit: it's not strictly green/environmental news, but there are often articles about that kind of thing

Well done for trying to avoid the Internet doom-spiral. Staying mentally healthy is important in this day-and-age. On Lemmy there's upliftingnews@lemmy.world and also Climate hope as someone else mentioned.

There's also these two websites that I often visit. The Futurecrunch Newsletter is definetely worth signing up to, which has a climate section:

https://futurecrunch.com/

https://www.goodnewsnetwork.org/