You can find the official link for Tentacles Thrive and other versions from the developer, Nonoplayer
Industry whispers point to an unannounced project from a splinter team of former Stellaris and Rain World developers. The working title, , is described as an "asymmetrical ecosystem simulator" where the player controls a growing mycelial-tentacular organism. Unlike traditional real-time strategy games, there are no rigid tech trees. Instead, physics-based tentacles grow in real time, responding to environmental stimuli, resource nodes, and—critically—other players’ entities. tentacles thrive v01 beta nonoplayer link
As of this writing, fewer than 200 individuals have reportedly accessed the v01 beta via valid nonoplayer links. The closed tester group refers to themselves as “The Mycelium.” Here are some anonymized reactions: You can find the official link for Tentacles