If you are looking for another self-hostable alternative to Slack, Rocket chat[0] is also worth looking at.
I wasn't involved in any of the Dev Ops aspect when my former employer used them, but the search function actually worked which is better than I can say for Slack.
Really? I have yet to use a single Slack-alike with search that actually works - including Slack, Teams and Mattermost. I mean they "work" in that the search results happen to include your terms too, but they give you the actual relevant message only about 10% of the time.
Rocket Chat does look nice! I quite liked Mattermost except for the mobile app being trash. How is the Rocket Chat mobile app?
I wasn't involved in any of the Dev Ops aspect when my former employer used them, but the search function actually worked which is better than I can say for Slack.
[0]https://github.com/RocketChat/Rocket.Chat/blob/develop/LICEN...