I’m working on a project that needs a similar approach to slack or discord. I know about matrix, but the person I’m working with said to be open to use a fediverse alternate when I tell them I didn’t want to use slack. I mention matrix and the fediverse as an alternative and they asked me a good fediverse option.
It’s needs to be good for team collaboration, easy to set and be able to maintain original images quality.
Are you willing to set up your own thing I recomend Mattermost. https://mattermost.com/
It’s open source, but I wouldn’t call it a fediverse alternative. But it’s still a good slack alternative.