I'm glad slack added this super useful popup, I didn't know what symbol this way, but the popup explained it !!
[Notice Regarding the Transfer of the mstdn.jp / mastodon.cloud Services] We have received several inquiries showing interest in a transfer following the announcement of the end of the mstdn.jp and mastodon.cloud services. As a result of subsequently evaluating the situation and making preparations, we have decided that the corresponding services will be transferred to Sujitech, LLC. on June 30. Thank you.